Category Archives: cURL and libcurl

curl and/or libcurl related

cURL and libcurl, Open Source

The curl 7 series reaches 60

curl 7.60.0 is released. Remember 7.59.0? This latest release cycle was a week longer than normal since the last was one week shorter and we had this particular release date adapted to my traveling last week. It gave us 63 days to cram things in, instead of the regular 56 days.

7.60.0 is a crazy version number in many ways. We’ve been working on the version 7 series since virtually forever (the year 2000) and there’s no version 8 in sight any time soon. This is the 174th curl release ever.

I believe we shouldn’t allow the minor number to go above 99 (because I think it will cause serious confusion among users) so we should come up with a scheme to switch to version 8 before 7.99.0 gets old. If we keeping doing a new minor version every eight weeks, which seems like the fastest route, math tells us that’s a mere 6 years away.

Numbers

In the 63 days since the previous release, we have done and had..

3 changes
111 bug fixes (total: 4,450)
166 commits (total: 23,119)
2 new curl_easy_setopt() options (total: 255)
1 new curl command line option (total: 214)
64 contributors, 36 new (total: 1,741)
42 authors (total: 577)
2 security fixes (total: 80)

What good does 7.60.0 bring?

Our tireless and fierce army of security researches keep hammering away at every angle of our code and this has again unveiled vulnerabilities in previously released curl code:

  1. FTP shutdown response buffer overflow: CVE-2018-1000300

When you tell libcurl to use a larger buffer size, that larger buffer size is not used for the shut down of an FTP connection so if the server then sends back a huge response during that sequence, it would buffer-overflow a heap based buffer.

2. RTSP bad headers buffer over-read: CVE-2018-1000301

The header parser function would sometimes not restore a pointer back to the beginning of the buffer, which could lead to a subsequent function reading out of buffer and causing a crash or potential information leak.

There are also two new features introduced in this version:

HAProxy protocol support

HAProxy has pioneered this simple protocol for clients to pass on meta-data to the server about where it comes from; designed to allow systems to chain proxies / reverse-proxies without losing information about the original originating client. Now you can make your libcurl-using application switch this on with CURLOPT_HAPROXYPROTOCOL and from the command line with curl’s new –haproxy-protocol option.

Shuffling DNS addresses

Over six years ago, I blogged on how round robin DNS doesn’t really work these days. Once upon the time the gethostbyname() family of functions actually returned addresses in a sort of random fashion, which made clients use them in an almost random fashion and therefore they were spread out on the different addresses. When getaddrinfo() has taken over as the name resolving function, it also introduced address sorting and prioritizing, in a way that effectively breaks the round robin approach.

Now, you can get this feature back with libcurl. Set CURLOPT_DNS_SHUFFLE_ADDRESSES to have the list of addresses shuffled after resolved, before they’re used. If you’re connecting to a service that offer several IP addresses and you want to connect to one of those addresses in a semi-random fashion, this option is for you.

There’s no command line option to switch this on. Yet.

Bug fixes

We did many bug fixes for this release as usual, but some of my favorite ones this time around are…

improved pending transfers for HTTP/2

libcurl-using applications that add more transfers than what can be sent over the wire immediately (usually because the application as set some limitation of the parallelism libcurl will do) can be held “pending” by libcurl. They’re basically kept in a separate queue until there’s a chance to send them off. They will then be attempted to get started when the streams than are in progress end.

The algorithm for retrying the pending transfers were quite naive and “brute-force” which made it terribly slow and in effective when there are many transfers waiting in the pending queue. This slowed down the transfers unnecessarily.

With the fixes we’ve landed in7.60.0, the algorithm is less stupid which leads to much less overhead and for this setup, much faster transfers.

curl_multi_timeout values with threaded resolver

When using a libcurl version that is built to use a threaded resolver, there’s no socket to wait for during the name resolving phase so we’ve often recommended users to just wait “a short while” during this interval. That has always been a weakness and an unfortunate situation.

Starting now, curl_multi_timeout() will return suitable timeout values during this period so that users will no longer have to re-implement that logic themselves. The timeouts will be slowly increasing to make sure fast resolves are detected quickly but slow resolves don’t consume too much CPU.

much faster cookies

The cookie code in libcurl was keeping them all in a linear linked list. That’s fine for small amounts of cookies or perhaps if you don’t manipulate them much.

Users with several hundred cookies, or even thousands, will in 7.60.0 notice a speed increase that in some situations are in the order of several magnitudes when the internal representation has changed to use hash tables and some good cleanups were made.

HTTP/2 GOAWAY-handling

We figure out some problems in libcurl’s handling of GOAWAY, like when an application wants to do a bunch of transfers over a connection that suddenly gets a GOAWAY so that libcurl needs to create a new connection to do the rest of the pending transfers over.

Turns out nginx ships with a config option named http2_max_requests that sets the maximum number of requests it allows over the same connection before it sends GOAWAY over it (and it defaults to 1000). This option isn’t very well explained in their docs and it seems users won’t really know what good values to set it to, so this is probably the primary reason clients see GOAWAYs where there’s no apparent good reason for them.

Setting the value to a ridiculously low value at least helped me debug this problem and improve how libcurl deals with it!

Repair non-ASCII support

We’ve supported transfers with libcurl on non-ASCII platforms since early 2007. Non-ASCII here basically means EBCDIC, but the code hasn’t been limited to those.

However, due to this being used by only a small amount of users and that our test infrastructure doesn’t test this feature good enough, we slipped recently and broke libcurl for the non-ASCII users. Work was put in and changes were landed to make sure that libcurl works again on these systems!

Enjoy 7.60.0! In 56 days there should be another release to play with…

cURL and libcurl

curl user survey 2018

The curl user survey 2018 is up. If you ever use curl or libcurl, please donate some of your precious time and provide your answers!

The curl user survey is an annual tradition since 2014 and it is one of our primary ways to get direct feedback from a larger audience about what’s good, what’s bad and what to focus on next in the curl project. Your input really helps us!

2018 survey

The survey will be up and available to fill in during 14 days, from May 15th until the end of May 28th. Please help us share this and ask your curl using friends to join in as well.

If you submitted data last year, make sure you didn’t miss the analysis of the 2017 survey.

cURL and libcurl, Open Source

Would you like some bold with those headers?

Displaying HTTP headers for a URL on the screen is one of those things people commonly use curl for.

curl -I example.com

To help your eyes separate header names from the corresponding values, I’ve been experimenting with a change that makes the header names get shown using a bold type face and the header values to the right of the colons to use the standard font.

Sending a HEAD request to the curl site could look like this:

This seemingly small change required an unexpectedly large surgery.

Now I want to turn this into a discussion if this is good enough, if we need more customization, how to make the code act on windows and perhaps how an option to explicitly enable/disable this should be named.

If you have ideas for any of that or other things around this feature, do comment in the PR.

The feature window for the next curl release is already closed so this change will not be considered for real until curl 7.61.0 at the earliest. Due for release in July 2018. So lots of time left to really “bike shed” all the details!

Update: the PR was merged into master on May 21st.

cURL and libcurl, Open Source

curl up 2018 summary

curl up 2018

The event that occurred this past weekend was the second time we gathered a bunch of curl enthusiasts and developers in the same physical room to discuss the past, the present and the future from a curl perspective.

Stockholm, Sweden, was the center of gravity this time when Goto 10 hosted our merry collective. Spring has finally arrived here and as the sun was out a lot, it made it a lovely weekend weather wise too. As a bonus, the little coffee shop on the premises was open all through both days. Just for us!

This time we were 22 peeps coming in from Sweden, Germany, UK, Spain, the US, and Czechia.

This is what it looked like (photos by me):

Talks

We had a bunch of presentations over the two days, done by a bunch of people. I recorded the screens and recorded the voice on most of them, and they’re available online. (Apologies for only recording a part of the screen for many of them!)

The talks were around how things work in curl or in the curl project, how people have used curl and a bit about upcoming technologies that we hope to get curl to support (soon?): QUIC, DOH, Alt-Svc, tests, CI, proxies, libcurl in Apache, using curl on a CDN, fuzzing curl, parsing email with curl etc.

Quiz

We rounded off the Saturday with a twelve question curl quiz. The winner, Fernando, managed to hit the right answer in 8 questions and did it faster than the competition. He got himself a signed copy of Everything curl the second print edition as a prize!

Sponsors

46 Elks was graciously sponsoring us with awesome food and t-shirts.

Sticker Mule provided us with stickers.

Goto 10 let us occupy their place during the weekend when it is otherwise closed!

This event was possible only thanks to their help!

2019

Several people asked me about next year already. I certainly hope we can run another curl up in 2019, but I don’t know yet where this should happen. Ideally, I would like to move it around to different countries to give different people the ability to show up easier, but I also value having a local “host” that can provide the room and facilities for us. I’ll send out probing questions about the 2019 location later this year. If you have a usable office or another suitable place that could host us, (preferably outside of Germany or Sweden), feel most welcome and encouraged to contact me!

(me, photographed by Christian Schmitz)

cURL and libcurl, Open Source

curl another host

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Sometimes you want to issue a curl command against a server, but you don’t really want curl to resolve the host name in the given URL and use that, you want to tell it to go elsewhere. To the “wrong” host, which in this case of course happens to be the right host. Because you know better.

Don’t worry. curl covers this as well, in several different ways…

Fake the host header

The classic and and easy to understand way to send a request to the wrong HTTP host is to simply send a different Host: header so that the server will provide a response for that given server.

If you run your “example.com” HTTP test site on localhost and want to verify that it works:

curl --header "Host: example.com" http://127.0.0.1/

curl will also make cookies work for example.com in this case, but it will fail miserably if the page redirects to another host and you enable redirect-following (--location) since curl will send the fake Host: header in all further requests too.

The --header option cleverly cancels the built-in provided Host: header when a custom one is provided so only the one passed in from the user gets sent in the request.

Fake the host header better

We’re using HTTPS everywhere these days and just faking the Host: header is not enough then. An HTTPS server also needs to get the server name provided already in the TLS handshake so that it knows which cert etc to use. The name is provided in the SNI field. curl also needs to know the correct host name to verify the server certificate against (server certificates are rarely registered for an IP address). curl extracts the name to use in both those case from the provided URL.

As we can’t just put the IP address in the URL for this to work, we reverse the approach and instead give curl the proper URL but with a custom IP address to use for the host name we set. The --resolve command line option is our friend:

curl --resolve example.com:443:127.0.0.1 https://example.com/

Under the hood this option populates curl’s DNS cache with a custom entry for “example.com” port 443 with the address 127.0.0.1, so when curl wants to connect to this host name, it finds your crafted address and connects to that instead of the IP address a “real” name resolve would otherwise return.

This method also works perfectly when following redirects since any further use of the same host name will still resolve to the same IP address and redirecting to another host name will then resolve properly. You can even use this option multiple times on the command line to add custom addresses for several names. You can also add multiple IP addresses for each name if you want to.

Connect to another host by name

As shown above, --resolve is awesome if you want to point curl to a specific known IP address. But sometimes that’s not exactly what you want either.

Imagine you have a host name that resolves to a number of different host names, possibly a number of front end servers for the same site/service. Not completely unheard of. Now imagine you want to issue your curl command to one specific server out of the front end servers. It’s a server that serves “example.com” but the individual server is called “host-47.example.com”.

You could resolve the host name in a first step before curl is used and use --resolve as shown above.

Or you can use --connect-to, which instead works on a host name basis. Using this, you can make curl replace a specific host name + port number pair with another host name + port number pair before the name is resolved!

curl --connect-to example.com:443:host-47.example.com:443 https://example.com/

Crazy combos

Most options in curl are individually controlled which means that there’s rarely logic that prevents you from using them in the awesome combinations that you can think of.

--resolve, --connect-to and --header can all be used in the same command line!

Connect to a HTTPS host running on localhost, use the correct name for SNI and certificate verification, but then still ask for a separate host in the Host: header? Sure, no problem:

curl --resolve example.com:443:127.0.0.1 https://example.com/ --header "Host: diff.example.com"

All the above with libcurl?

When you’re done playing with the curl options as described above and want to convert your command lines to libcurl code instead, your best friend is called --libcurl.

Just append --libcurl example.c to your command line, and curl will generate the C code template for you in that given file name. Based on that template, making use of  that code correctly is usually straight-forward and you’ll get all the options to read up in a convenient way.

Good luck!

Update: thanks to @Manawyrm, I fixed the ndash issues this post originally had.

cURL and libcurl, Network, Open Source, Security

Play TLS 1.3 with curl

The IESG recently approved the TLS 1.3 draft-28 for proposed standard and we can expect the real RFC for this protocol version to appear soon (within a few months probably).

TLS 1.3 has been in development for quite some time by now, and a lot of TLS libraries already support it to some extent. At varying draft levels.

curl and libcurl has supported an explicit option to select TLS 1.3 since curl 7.52.0 (December 2016) and assuming you build curl to use a TLS library with support, you’ve been able to use TLS 1.3 with curl since at least then. The support has gradually been expanded to cover more and more libraries since then.

Today, curl and libcurl support speaking TLS 1.3 if you build it to use one of these fine TLS libraries of a recent enough version:

  • OpenSSL
  • BoringSSL
  • libressl
  • NSS
  • WolfSSL
  • Secure Transport (on iOS 11 or later, and macOS 10.13 or later)

GnuTLS seems to be well on their way too. TLS 1.3 support exists in the GnuTLS master branch on gitlab.

curl’s TLS 1.3-support makes it possible to select TLS 1.3 as preferred minimum version.

cURL and libcurl, Open Source

Twenty years, 1998 – 2018

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Do you remember this exact day, twenty years ago? March 20, 1998. What exactly happened that day? I’ll tell you what I did then.

First a quick reminder of the state of popular culture at the time: three days later, on the 23rd, the movie Titanic would tangent the record and win eleven academy awards. Its theme song “My heart will go on” was in the top of the music charts around this time.

I was 27 years old and I worked full-time as a software engineer, mostly with embedded systems. I had already been developing software as a profession for several years then. At this moment in time I was involved as a consultant in a (rather boring) project for Ericsson Telecom ETX, in Nacka Strand in the south eastern general Stockholm area.

At some point during that Friday (I don’t remember the details, but presumably it happened during the late evening), I packaged up the source code of the URL transfer tool we were working on and uploaded it to my personal web site to share it with the world. It was the first release ever of the project under the new name: curl. The tool was already supporting HTTP, FTP and GOPHER – including uploads for the two first protocols.

It would take more than a year after this day until we started hosting the curl project on its own dedicated web site. curl.haxx.nu went live in August 1999, and it was changed again to curl.haxx.se in June the following year, a URL and name we’ve kept since.

(this is the first curl logo we used, made in 1998 by Henrik Hellerstedt)

In my flat in Solna (just north of Stockholm, Sweden) I already then spent a lot of spare time, mostly late nights, in front of my computer. Back then, an Intel Pentium 120Mhz based desktop PC with a huge 19″ Nokia CRT monitor, on which I dialed up to my work’s modem pool to access the Internet and to log in to the Unix machines there on which I did a lot of the early curl development. On SunOS, Solaris and Linux.

In Stockholm, that Friday started out with sub-zero degrees Celsius but the temperature climbed up to a few positive degrees during the day and there was no snow on the ground. Pretty standard March weather in Stockholm. This is usually a period when the light is slowly coming back (winters are really dark here) but the temperatures remind us that spring still isn’t quite here.

curl 4.0 was just a little more than 2000 lines of C code. It featured 23 command line options. curl 4.0 introduced support for the FTP PORT command and now it could do ftp uploads that append to the remote file. The version number was bumped up from the 3.12 which was the last version number used by the tool under the old name, urlget.

This is what the web site looked like in December 1998, the oldest capture I could find. Extracted from archive.org so unfortunately two graphical elements are missing!

It was far from an immediate success. An old note mentions how curl 4.8 (released the summer of 1998) was downloaded more than 300 times from the site. In August 1999, we counted 1300 weekly visits on the web site. It took time to get people to discover curl and make it into the tool users wanted. By September 1999 curl had already grown to 15K lines of code

In August 2000 we shipped the first version of libcurl: all the networking transfer powers of curl in a library, ready to be used by your applications. PHP was one of the absolutely first users of libcurl and that certainly helped to drive the early use.

A year later, in August 2001, when Apple started shipping curl by default in Mac OS X 10.1 curl was already widely available in Linux and BSD package collections.

By June 2002, we counted 13000 weekly visits on the site and we had grown to 35K lines of code. And it would not stop there…

Twenty years is both nothing at all and at the same time what feels like an eternity. Just three weeks before curl 4.0 shipped, Mozilla was founded. Google wasn’t founded until six months after. This was long before Facebook or Twitter had even been considered. Certainly a different era. Even the term open source was coined just a month prior to this curl release.

Growth factors over 20 years in the project:

Supported protocols: 7.67x
Command line options: 9x
Lines of code: 75x
Contributors: 100x
Weekly web site visitors: 1,400x
End users using (something that runs) the code: 4,000,000x
Stickers with the curl logo: infinity

Twenty years since the first ever curl release. Of course, it took time to make that first release too so the work is older. curl is the third name or incarnation of the project that I first got involved with already in late 1996…

 

cURL and libcurl, Open Source, Security

GAAAAAH

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That’s the thought that ran through my head when I read the email I had just received.

GAAAAAAAAAAAAH

You know the feeling when the realization hits you that you did something really stupid? And you did it hours ago and people already noticed so its too late to pretend it didn’t happen or try to cover it up and whistle innocently. Nope, none of those options were available anymore. The truth was out there.

I had messed up royally.

What triggered this sudden journey of emotions and sharp sense of pain in my soul, was an email I received at 10:18, Friday March 9 2018. The encrypted email pointed out to me in clear terms that there was information available publicly on the curl web site about the security vulnerabilities that we intended to announce in association with the next curl release, on March 21. (The person who emailed me is a member of a group that was informed by me about these issues ahead of time.)

In the curl project, we never reveal nor show any information about known security flaws until we ship fixes for them and publish their corresponding security advisories that explain the flaws, the risks, the fixes and work-arounds in detail. This of course in the name of keeping users safe. We don’t want bad guys to learn about problems and flaws until we also offer fixes for them. That is, unless you screw up like me.

It took me a few minutes until I paused my work I was doing at the moment and actually read the email, but once I did I acted immediately and at 10:24 I had reverted the change on the web site and purged the URL from the CDN so the information was no longer publicly visible there.

The entire curl web site is however kept in a public git repository, so while the sensitive information was no longer immediately notable on the site, it was still out of the bag and there was just no taking it back. Not to mention that we don’t know how many people that already updated their git clones etc.

I pushed the particular file containing the “extra information” to the web site’s git repository at 01:26 CET the same early morning and since the web site updates itself in a cronjob every 20 minutes we know the information became available just after 01:40. At which time I had already gone to bed.

The sensitive information was displayed on the site for 8 hours and 44 minutes. The security page table showed these lines at the top:

# Vulnerability Date First Last CVE CWE
78 RTSP RTP buffer over-read February 20, 2018 7.20.0 7.58.0 CVE-2018-1000122 CWE-126: Buffer Over-read
77 LDAP NULL pointer dereference March 06, 2018 7.21.0 7.58.0 CVE-2018-1000121 CWE-476: NULL Pointer Dereference
76 FTP path trickery leads to NIL byte out of bounds write March 21, 2018 7.12.3 7.58.0 CVE-2018-1000120 CWE-122: Heap-based Buffer Overflow

I only revealed the names of the flaws and their corresponding CWE (Common Weakness Enumeration) numbers, the full advisories were thankfully not exposed, the links to them were broken. (Oh, and the date column shows the dates we got the reports, not the date of the fixed release which is the intention.) We still fear that the names alone plus the CWE descriptions might be enough for intelligent attackers to figure out the rest.

As a direct result of me having revealed information about these three security vulnerabilities, we decided to change the release date of the pending release curl 7.59.0 to happen one week sooner than previously planned. To reduce the time bad actors would be able to abuse this information for malicious purposes.

How exactly did it happen?

When approaching a release day, I always create local git branches  called next-release in both the source and the web site git repositories. In the web site’s next-release branch I add the security advisories we’re working on and I add/update meta-data about these vulnerabilities etc. I prepare things in that branch that should go public on the release moment.

We’ve added CWE numbers to our vulnerabilities for the first time (we are now required to provide them when we ask for CVEs). Figuring out these numbers for the new issues made me think that I should also go back and add relevant CWE numbers to our old vulnerabilities as well and I started to go back to old issues and one by one dig up which numbers to use.

After having worked on that for a while, for some of the issues it is really tricky to figure out which CWE to use, I realized the time was rather late.

– I better get to bed and get some sleep so that I can get some work done tomorrow as well.

Then I realized I had been editing the old advisory documents while still being in the checked out next-release branch. Oops, that was a mistake. I thus wanted to check out the master branch again to push the update from there. git then pointed out that the vuln.pm file couldn’t get moved over because of reasons. (I forget the exact message but it it happened because I had already committed changes to the file in the new branch that weren’t present in the master branch.)

So, as I wanted to get to bed and not fight my tools, I saved the current (edited) file in a different name, checked out the old file version from git again, changed branch and moved the renamed file back to vuln.pm again (without a single thought that this file now contained three lines too many that should only be present in the next-release branch), committed all the edited files and pushed them all to the remote git repository… boom.

You’d think I would…

  1. know how to use git correctly
  2. know how to push what to public repos
  3. not try to do things like this at 01:26 in the morning

curl 7.59.0 and these mentioned security vulnerabilities were made public this morning.

cURL and libcurl, Open Source

Here’s curl 7.59.0

We ship curl 7.59.0 exactly 49 days since the previous release (a week shorter than planned because of reasons). Download it from here. Full changelog is here.

In these 49 days, we have done and had..

6 changes(*)
78 bug fixes (total: 4337)
149 commits (total: 22,952)
45 contributors, 20 new (total: 1,702)
29 authors (total: 552)
3 security fixes (total: 78)

This time we’ve fixed no less than three separate security vulnerabilities:

  1. FTP path trickery security issue
  2. LDAP NULL dereference
  3. RTSP RTP buffer over-read

(*) = changes are things that don’t fix existing functionality but actually add something new to curl/libcurl. New features mostly.

The new things time probably won’t be considered as earth shattering but still a bunch of useful stuff:

–proxy-pinnedpubkey

The ability to specified a public key pinning has been around for a while for regular servers, and libcurl has had the ability to pin proxies’ keys as well. This change makes sure that users of the command line tool also gets that ability. Make sure your HTTPS proxy isn’t MITMed!

CURLOPT_TIMEVALUE_LARGE

Part of our effort to cleanup our use of ‘long’ variables internally to make sure we don’t have year-2038 problems, this new option was added.

CURLOPT_RESOLVE

This popular libcurl option that allows applications to populate curl’s DNS cache with custom IP addresses for host names were improved and now you can add multiple addresses for host names. This allows transfers using this to even more work like as if it used normal name resolves.

CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS

As a true HTTP swiss-army knife tool and library, you can toggle and tweak almost all aspects, timers and options that are used. This libcurl option has a new corresponding curl command line option, and allows the user to set the timeout time for how long after the initial (IPv6) connect call is done until the second (IPv4) connect is invoked in the happy eyeballs connect procedure. The default is 200 milliseconds.

Bug fixes!

As usual we fixed things all over. Big and small. Some of the ones that I think stuck out a little were the fix for building with OpenSSL 0.9.7 (because you’d think that portion of users should be extinct by now) and the fix to make configure correctly detect OpenSSL 1.1.1 (there are beta releases out there).

Some application authors will appreciate that libcurl now for the most part detects if it gets called from within one of its own callbacks and returns an error about it. This is mostly to save these users from themselves as doing this would already previously risk damaging things. There are some functions that are still allowed to get called from within callbacks.

cURL and libcurl

Why is your email in my car?

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I got this email in German…

Subject: Warumfrage

Schönen guten Tag

Ich habe auf meinem Navi aus meinem Auto einen Riesentext wo unter anderem Ihre Mailadresse zu sehen ist?

Können Sie mich schlau machen was es damit auf sich hat ?

… which translated into English says:

I have a huge text on my sat nav in my car where, among other things, your email address can be seen?

Can you tell me what this is all about?

I replied (in English) to the question, explained how I’m the main author of curl and how his navigation system is probably using this. I then asked what product or car he saw my email in and if he could send me a picture of my email being there.

He responded quickly and his very brief answer only says it is a Toyota Verso from 2015. So I put an image of such a car on the top of this post.