Category Archives: Technology

Really everything related to technology

a Google grant for libcurl work

Earlier this year I was the recipient of a monetary Google patch grant with the expressed purpose of improving security in libcurl.

This was an upfront payout under this Google program describing itself as “an experimental program that rewards proactive security improvements to select open-source projects”.

I accepted this grant for the curl project and I intend to keep working fiercely on securing curl. I recognize the importance of curl security as curl remains one of the most widely used software components in the world, and even one that is doing network data transfers which typically is a risky business. curl is responsible for a measurable share of all Internet transfers done over the Internet an average day. My job is to make sure those transfers are done as safe and secure as possible. It isn’t my only responsibility of course, as I have other tasks to attend to as well, but still.

Do more

Security is already and always a top priority in the curl project and for myself personally. This grant will of course further my efforts to strengthen curl and by association, all the many users of it.

What I will not do

When security comes up in relation to curl, some people like to mention and propagate for other programming languages, But curl will not be rewritten in another language. Instead we will increase our efforts in writing good C and detecting problems in our code earlier and better.

Proactive counter-measures

Things we have done lately and working on to enforce everywhere:

String and buffer size limits – all string inputs and all buffers in libcurl that are allowed to grow now have a maximum allowed size, that makes sense. This stops malicious uses that could make things grow out of control and it helps detecting programming mistakes that would lead to the same problems. Also, by making sure strings and buffers are never ridiculously large, we avoid a whole class of integer overflow risks better.

Unified dynamic buffer functions – by reducing the number of different implementations that handle “growing buffers” we reduce the risk of a bug in one of them, even if it is used rarely or the spot is hard to reach with and “exercise” by the fuzzers. The “dynbuf” internal API first shipped in curl 7.71.0 (June 2020).

Realloc buffer growth unification – pretty much the same point as the previous, but we have earlier in our history had several issues when we had silly realloc() treatment that could lead to bad things. By limiting string sizes and unifying the buffer functions, we have reduced the number of places we use realloc and thus we reduce the number of places risking new realloc mistakes. The realloc mistakes were usually in combination with integer overflows.

Code style – we’ve gradually improved our code style checker (checksrc.pl) over time and we’ve also gradually made our code style more strict, leading to less variations in code, in white spacing and in naming. I’m a firm believer this makes the code look more coherent and therefore become more readable which leads to fewer bugs and easier to debug code. It also makes it easier to grep and search for code as you have fewer variations to scan for.

More code analyzers – we run every commit and PR through a large number of code analyzers to help us catch mistakes early, and we always remove detected problems. Analyzers used at the time of this writing: lgtm.com, Codacy, Deepcode AI, Monocle AI, clang tidy, scan-build, CodeQL, Muse and Coverity. That’s of course in addition to the regular run-time tools such as valgrind and sanitizer builds that run the entire test suite.

Memory-safe components – curl already supports getting built with a plethora of different libraries and “backends” to cater for users’ needs and desires. By properly supporting and offering users to build with components that are written in for example rust – or other languages that help developers avoid pitfalls – future curl and libcurl builds could potentially avoid a whole section of risks. (Stay tuned for more on this topic in a near future.)

Reactive measures

Recognizing that whatever we do and however tight ship we run, we will continue to slip every once in a while, is important and we should make sure we find and fix such slip-ups as good and early as possible.

Raising bounty rewards. While not directly fixing things, offering more money in our bug-bounty program helps us get more attention from security researchers. Our ambition is to gently drive up the reward amounts progressively to perhaps multi-thousand dollars per flaw, as long as we have funds to pay for them and we mange keep the security vulnerabilities at a reasonably low frequency.

More fuzzing. I’ve said it before but let me say it again: fuzzing is really the top method to find problems in curl once we’ve fixed all flaws that the static analyzers we use have pointed out. The primary fuzzing for curl is done by OSS-Fuzz, that tirelessly keeps hammering on the most recent curl code.

Good fuzzing needs a certain degree of “hand-holding” to allow it to really test all the APIs and dig into the dustiest corners, and we should work on adding more “probes” and entry-points into libcurl for the fuzzer to make it exercise more code paths to potentially detect more mistakes.

See also my presentation testing curl for security.

Fiber breakage, day 4

Aaaaaaah.

Warning to sensitive viewers, this is seriously scary stuff. So this happened Monday and I’m still to see any service people show up here to help me restore my life (I of course requested help within minutes). What you see here is a fiber that’s been cut off – the fiber that goes into my house. Turns out even a small excavator can do great damage. Who knew?!

We’re now forced to survive on LTE only and the household suddenly has gotten a much bigger appreciation for the regular 1000/1000 mbit connectivity…

Friday 14th: a service guy was here, repaired the “cable” but failed to “blow in” a new fiber into the tube. According to him, there’s some kind of dust/rubbish now in the tube that’s in the way so it became a larger issue. He had to take off again and says they need to come back next week…

QUIC with wolfSSL

We have started the work on extending wolfSSL to provide the necessary API calls to power QUIC and HTTP/3 implementations!

Small, fast and FIPS

The TLS library known as wolfSSL is already very often a top choice when users are looking for a small and yet very fast TLS stack that supports all the latest protocol features; including TLS 1.3 support – open source with commercial support available.

As manufacturers of IoT devices and other systems with memory, CPU and footprint constraints are looking forward to following the Internet development and switching over to upcoming QUIC and HTTP/3 protocols, wolfSSL is here to help users take that step.

A QUIC reminder

In case you have forgot, here’s a schematic view of HTTPS stacks, old vs new. On the right side you can see HTTP/3, QUIC and the little TLS 1.3 box there within QUIC.

ngtcp2

There are no plans to write a full QUIC stack. There are already plenty of those. We’re talking about adjustments and extensions of the existing TLS library API set to make sure wolfSSL can be used as the TLS component in a QUIC stack.

One of the leading QUIC stacks and so far the only one I know of that does this, ngtcp2 is written to be TLS library agnostic and allows different TLS libraries to be plugged in as different backends. I believe it makes perfect sense to make such a plugin for wolfSSL to be a sensible step as soon as there’s code to try out.

A neat effect of that, would be that once wolfSSL works as a backend to ngtcp2, it should be possible to do full-fledged HTTP/3 transfers using curl powered by ngtcp2+wolfSSL. Contact us with other ideas for QUIC stacks you would like us to test wolfSSL with!

FIPS 140-2

We expect wolfSSL to be the first FIPS-based implementation to add support for QUIC. I hear this is valuable to a number of users.

When

This work begins now and this is just a blog post of our intentions. We and I will of course love to get your feedback on this and whatever else that is related. We’re also interested to get in touch with people and companies who want to be early testers of our implementation. You know where to find us!

I can promise you that the more interest we can sense to exist for this effort, the sooner we will see the first code to test out.

It seems likely that we’re not going to support any older TLS drafts for QUIC than draft-29.

qlog with curl

I want curl to be on the very bleeding edge of protocol development to aid the Internet protocol development community to test out protocols early and to work out kinks in the protocols and server implementations using curl’s vast set of tools and switches.

For this, curl supported HTTP/2 really early on and helped shaping the protocol and testing out servers.

For this reason, curl supports HTTP/3 already since August 2019. A convenient and well-known client that you can then use to poke on your brand new HTTP/3 servers too and we can work on getting all the rough edges smoothed out before the protocol is reaching its final state.

QUIC tooling

One of the many challenges QUIC and HTTP/3 have is that with a new transport protocol comes entirely new paradigms. With new paradigms like this, we need improved or perhaps even new tools to help us understand the network flows back and forth, to make sure we all have a common understanding of the protocols and to make sure we implement our end-points correctly.

QUIC only exists as an encrypted-only protocol, meaning that we can no longer easily monitor and passively investigate network traffic like before, QUIC also encrypts more of the protocol than TCP + TLS do, leaving even less for an outsider to see.

The current QUIC analyzer tool lineup gives us two options.

Wireshark

We all of course love Wireshark and if you get a very recent version, you’ll be able to decrypt and view QUIC network data.

With curl, and a few other clients, you can ask to get the necessary TLS secrets exported at run-time with the SSLKEYLOGFILE environment variable. You’ll then be able to see every bit in every packet. This way to extract secrets works with QUIC as well as with the traditional TCP+TLS based protocols.

qvis/qlog

The qvis/qlog site. If you find the Wireshark network view a little bit too low level and leaving a lot for you to understand and draw conclusions from, the next-level tool here is the common QUIC logging format called qlog. This is an agreed-upon common standard to log QUIC traffic, which the accompanying qvis web based visualizer tool that lets you upload your logs and get visualizations generated. This becomes extra powerful if you have logs from both ends!

Starting with this commit (landed in the git master branch on May 7, 2020), all curl builds that support HTTP/3 – independent of what backend you pick – can be told to output qlogs.

Enable qlogging in curl by setting the new standard environment variable QLOGDIR to point to a directory in which you want qlogs to be generated. When you run curl then, you’ll get files creates in there named as [hex digits].log, where the hex digits is the “SCID” (Source Connection Identifier).

Credits

qlog and qvis are spear-headed by Robin Marx. qlogging for curl with Quiche was pushed for by Lucas Pardue and Alessandro Ghedini. In the ngtcp2 camp, Tatsuhiro Tsujikawa made it very easy for me to switch it on in curl.

The top image is snapped from the demo sample on the qvis web site.

Report: curl’s bug bounty one year in

On April 22nd 2019, we announced our current, this, incarnation of the curl bug bounty. In association with Hackerone we now run the program ourselves, primarily funded by gracious sponsors. Time to take a closer look at how the first year of bug bounty has been!

Number of reports

We’ve received a total of 112 reports during this period.

On average, we respond with a first comment to reports within the first hour and we triage them on average within the first day.

Out of the 112 reports, 6 were found actual security problems.

Total amount of reports vs actual security problems, per month during the first year of the curl hackerone bug bounty program.

Bounties

All confirmed security problems were rewarded a bounty. We started out a bit careful with the amounts but we are determined to raise them as we go along and we’ve seen that there’s not really a tsunami coming.

We’ve handed out 1,400 USD so far, which makes it an average of 233 USD per confirmed report. The top earner got two reports rewarded and received 450 USD from us. So far…

But again: our ambition is to significantly raise these amounts going forward.

Trends

The graph above speaks clearly: lots of people submitted reports when we opened up and the submission frequency has dropped significantly over the year.

A vast majority of the 112 reports we’ve received have were more or less rubbish and/or more or less automated reports. A large amount of users have reported that our wiki can be edited by anyone (which I consider to be a fundamental feature of a wiki) or other things that we’ve expressly said is not covered by the program: specific details about our web hosting, email setup or DNS config.

A rough estimate says that around 80% of the reports were quickly dismissed as “out of policy” – ie they reported stuff that we documented is not covered by the bug bounty (“Sirs, we can figure out what http server that’s running” etc). The curl bug bounty covers the products curl and libcurl, thus their source code and related specifics.

Bounty funds

curl has no ties to any organization. curl is not owned by any corporation. curl is developed by individuals. All the funds we have in the project are graciously provided to us by sponsors and donors. The curl funds are handled by the awesome Open Collective.

Security is of utmost importance to us. It trumps all other areas, goals and tasks. We aim to produce solid and secure products for the world and we act as swiftly and firmly as we can on all reported security problems.

Security vulnerability trends

We have not published a single CVE for curl yet this year (there was one announced, CVE-2019-15601 but after careful considerations we have backpedaled on that, we don’t consider it a flaw anymore and the CVE has been rejected in the records.)

As I write this, there’s been exactly 225 days since the latest curl CVE was published and we’re aiming at shipping curl 7.70.0 next week as the 6th release in a row without a security vulnerability to accompany it. We haven’t done 6 “clean” consecutive release like this since early 2013!

Looking at the number of CVEs reported in the curl project per year, we can of course see that 2016 stands out. That was the year of the security audit that ended up the release of curl 7.51.0 with no less than eleven security vulnerabilities announced and fixed. Better is of course the rightmost bar over the year 2020 label. It is still non-existent!

The most recent CVEs per year graph is always found: here.

As you can see in the graph below, the “plateau” in the top right is at 92 published CVEs. The previous record holder for longest period in the project without a CVE ended in February 2013 (with CVE-2013-0249) at 379 days.

2013 was however quite a different era for curl. Less code, much less scrutinizing, no bug bounty, lesser tools, no CI jobs etc.

Number of published CVEs in the curl project over time. The updated graph is always found: here.

Are we improving?

Is curl getting more secure?

We have more code and support more protocols than ever. We have a constant influx of new authors and contributors. We probably have more users than ever before in history.

At the same time we offer better incentives than ever before for people to report security bugs. We run more CI jobs than ever that run more and more test cases while code analyzers and memory debugging are making it easier to detect problems earlier. There are also more people looking for security bugs in curl than ever before.

Jinx?

I’m under no illusion that there aren’t more flaws to find, report and fix. We’re all humans and curl is still being developed at a fairly high pace.

Please report more security bugs!

Credits

Top image by Luisella Planeta Leoni from Pixabay

curl is not removing FTP

FTP is going out of style.

The Chrome team has previously announced that they are deprecating and removing support for FTP.

Mozilla also announced their plan for the deprecation of FTP in Firefox.

Both browsers have paused or conditioned their efforts to not take the final steps during the Covid-19 outbreak, but they will continue and the outcome is given: FTP support in browsers is going away. Soon.

curl

curl supported both uploads and downloads with FTP already in its first release in March 1998. Which of course was many years before either of those browsers mentioned above even existed!

In the curl project, we work super hard and tirelessly to maintain backwards compatibility and not break existing scripts and behaviors.

For these reasons, curl will not drop FTP support. If you have legacy systems running FTP, curl will continue to have your back and perform as snappy and as reliably as ever.

FTP the protocol

FTP is a protocol that is quirky to use over the modern Internet mostly due to its use of two separate TCP connections. It is unencrypted in its default version and the secured version, FTPS, was never supported by browsers. Not to mention that the encrypted version has its own slew of issues when used through NATs etc.

To put it short: FTP has its issues and quirks.

FTP use in general is decreasing and that is also why the browsers feel that they can take this move: it will only negatively affect a very minuscule portion of their users.

Legacy

FTP is however still used in places. In the 2019 curl user survey, more than 29% of the users said they’d use curl to transfer FTP within the last two years. There’s clearly a long tail of legacy FTP systems out there. Maybe not so much on the public Internet anymore – but in use nevertheless.

Alternative protocols?

SFTP could have become a viable replacement for FTP in these cases, but in practice we’ve moved into a world where HTTPS replaces everything where browsers are used.

Credits

Train image by D Thory from Pixabay

Warning: curl users on Windows using FILE://

The Windows operating system will automatically, and without any way for applications to disable it, try to establish a connection to another host over the network and access it (over SMB or other protocols), if only the correct file path is accessed.

When first realizing this, the curl team tried to filter out such attempts in order to protect applications for inadvertent probes of for example internal networks etc. This resulted in CVE-2019-15601 and the associated security fix.

However, we’ve since been made aware of the fact that the previous fix was far from adequate as there are several other ways to accomplish more or less the same thing: accessing a remote host over the network instead of the local file system.

The conclusion we have come to is that this is a weakness or feature in the Windows operating system itself, that we as an application and library cannot protect users against. It would just be a whack-a-mole race we don’t want to participate in. There are too many ways to do it and there’s no knob we can use to turn off the practice.

We no longer consider this to be a curl security flaw!

If you use curl or libcurl on Windows (any version), disable the use of the FILE protocol in curl or be prepared that accesses to a range of “magic paths” will potentially make your system try to access other hosts on your network. curl cannot protect you against this.

We have updated relevant curl and libcurl documentation to make users on Windows aware of what using FILE:// URLs can trigger (this commit) and posted a warning notice on the curl-library mailing list.

Previous security advisory

This was previously considered a curl security problem, as reported in CVE-2019-15601. We no longer consider that a security flaw and have updated that web page with information matching our new findings. I don’t expect any other CVE database to update since there’s no established mechanism for updating CVEs!

Credits

Many thanks to Tim Sedlmeyer who highlighted the extent of this issue for us.

Remote-exploiting curl

In a Blackhat 2019 presentation, three gentlemen from the Tencent Blade Team explained how they found and managed to exploit two curl flaws. Both related to NTLM over HTTP. The “client version Heartbleed” as they call it.

Reported responsibly

The Tencent team already reported the bugs responsibly to us and we already fixed them back in February 2019, but the talk is still very interesting I think.

From my point of view, as I have already discussed these bugs with the team when they were reported us and when I worked on fixing them, I find it very interesting and educational to learn more about how exactly they envision an attacker would go about and exploit them in practice. I have much too bad imagination sometimes to really think of how bad exactly the problems can end up when a creative attacker gets to play with them.

The security issues

The two specific issues these stellar gents found are already fixed since curl 7.64.0 and you can read all the gory details about them here: CVE-2018-16890 and CVE-2019-3822. The latter is clearly the worse issue.

For all I know, these exploits have never been seen or reported to happen in real life.

Upgrade?

Luckily, most distros that ship older curl versions still back-port and apply later security patches so even if you may see that you have an older curl version installed on your system, chances are it has already been patched. Of course there’s also a risk that it hasn’t, so you should probably make sure rather than presume…

The video

The slides from their presentation. (The talk also details SQLite issues but they’re completely separate from the curl ones.)

Bug Bounty?

Unfortunately, I’m sorry to admit that these excellent friends of ours did not get a bug bounty from us! 🙁

We got their reports before our bug bounty was setup and we didn’t have neither the means nor the methods to reward them back then. If someone would report such serious bugs now, only a year later, we would probably reward new such findings with several thousand dollars.

On NTLM

NTLM was always wrong, bad and a hack. It’s not an excuse for having bugs in our code but man if someone could just please make that thing go away…

HTTP/3 for everyone

FOSDEM 2020 is over for this time and I had an awesome time in Brussels once again.

Stickers

I brought a huge collection of stickers this year and I kept going back to the wolfSSL stand to refill the stash and it kept being emptied almost as fast. Hundreds of curl stickers were given away! The photo on the right shows my “sticker bag” as it looked before I left Sweden.

Lesson for next year: bring a larger amount of stickers! If you missed out on curl stickers, get in touch and I’ll do my best to satisfy your needs.

The talk

“HTTP/3 for everyone” was my single talk this FOSDEM. Just two days before the talk, I landed updated commits in curl’s git master branch for doing HTTP/3 up-to-date with the latest draft (-25). Very timely and I got to update the slide mentioning this.

As I talked HTTP/3 already last year in the Mozilla devroom, I also made sure to go through the slides I used then to compare and make sure I wouldn’t do too much of the same talk. But lots of things have changed and most of the content is updated and different this time around. Last year, literally hundreds of people were lining up outside wanting to get into room when the doors were closed. This year, I talked in the room Janson, which features 1415 seats. The biggest one on campus. It was pack full!

It is kind of an adrenaline rush to stand in front of such a wall of people. At one time in my talk I paused for a brief moment and then I felt I could almost hear the complete silence when a huge amount of attentive faces captured what I had to say.

The audience, photographed by Sidsel Jensen who had to sit in the stairs…
Photo by Mirza Krak
Photo by Wolfgang Gassler

I got a lot of positive feedback on the presentation. I also thought that my decision to not even try to take question in the big room was a correct and I ended up talking and discussing details behind the scene for a good while after my talk was done. Really fun!

The video

The video is also available from the FOSDEM site in webm and mp4 formats.

The slides

If you want the slides only, run over to slideshare and view them.