Tag Archives: Mac OS X

Anatomy of a ghost CVE

“The Lord giveth and the Lord taketh away.”

Job 1:21

On March 16 2022, the curl security team received an email in which the reporter highlighted an Apple web page. What can you tell us about this?

I hadn’t seen it before. On this page with the title “About the security content of macOS Monterey 12.3”, said to have been published just two days prior, Apple mentions recent package upgrades and the page lists a bunch of products and what security fixes that were done for them in this update. Among the many products listed, curl is mentioned.

This is what the curl section of the page looked like:

Screenshot from March 17, 2022

In the curl project we always make all CVEs public with as much detail as we can possibly extract and provide about them. We take great pride in being the best in class in security flaw information and transparency.

Apple listed four CVE fixed. The three first IDs we immediately recognized from the curl security page. The last one however, was a surprise. What was that?

CVE-2022-22623

This is not a CVE published by the curl project. The curl project has in fact not shipped any CVE at all in 2022 (yet) so that’s easy to spot. When we looked at the MITRE registration for the ID, it also didn’t disclose any clues really. Not that it was expected to. It did show it was created on January 5 though, so it wasn’t completely new.

Was it a typo?

I compared this number to other recent CVE numbers announced from curl and I laid eyes on CVE-2021-22923 which had just two digits changed. Did they perhaps mean that CVE?

The only “problem” with that CVE is that it was in regards to Metalink and I don’t think Apple ever shipped their curl package with metalink support so therefore they wouldn’t have fixed a Metalink problem. So probably not a typo for that number at least!

I reached out to a friend at Apple as well with an email to Apple Product Security.

Security is our number one priority

In the curl project, we take security seriously. The news that there might be a security problem in curl that we haven’t been told about and that looks like it was about to get public sooner or later was of course somewhat alarming and something we just needed to get to the bottom of. It was also slightly disappointing that a large vendor and packager of curl since over 20 years would go about it this way and jab this into our back.

No source code

Apple has not made the source code for their macOS 12.3 version and the packages they use in there public, so there was no way for us to run diffs or anything to check for the exact modifications that this claimed fix would’ve resulted in.

Apple said so

Several “security websites” (the quotes are there to indicate that clearly these sites are more security in the name than in reality) immediately posted details about this “vulnerability”. Some of them with CVSS scores and CWE numbers , explaining how this problem can hurt users. Obviously completely made up since none of that info was made available by any first party sources anywhere. Not from Apple and not from the curl project. If you now did a web search on that CVE number, several of the top search results linked to such sites providing details – obviously made up from thin air.

As I think these sites don’t add much value to humanity, I won’t link to them here but instead I will show you a screenshot from such an article to show you what a made up CVE number posted by Apple can make people claim:

Screenshot from exploitone.com

At 23:28 (my time zone) on the 17th, my Apple friend responded saying they had forwarded the issue to “the right team”.

The Apple Product Security team I also emailed about this issue, answered at 00:23 (still my time) on the 18th saying “we are looking into this and will provide an update soon when we have more information.”

The MITRE page got more details

The MITRE CVE page from March 21st

After the weekend passed with no response, I looked back again on the MITRE page for the CVE in question and it had then gotten populated with additional curl details; mentioning Apple as CNA and now featuring links back to the Apple page! Now it really started to look like the CVE was something real that Apple (or someone) had registered but not told us about. It included real curl related snippets like this:

Multiple issues were addressed by updating to curl version 7.79.1. This issue is fixed in macOS Monterey 12.3. Multiple issues in curl.

Please tell us more details

On Monday the 21st, I continued to get questions about this CVE. Among others, from a member of a major European ISP’s CERT team curious about this CVE as they couldn’t find any specific information about this issue either and they were concerned they might have this vulnerability in the curl versions they run. They of course (rightfully) assumed that I would know about curl CVEs.

It turns out that when a major company randomly mentions a new CVE, it actually has an impact on the world!

Gone!

At around 20:30 on March 21st, someone on Twitter spotted that the ghost CVE had been removed from Apple’s web page and it only listed three issues (and a mention that the section had been updated). At 21:39 I get an email response from Apple Product Security:

Thank you for reaching out to us about the error with this CVE on our security advisory. We’ve updated our site and requested that MITRE reject CVE-2022-22623 on their end.

Please let us know if you have any questions.

Screenshot from March 21, 2022

The reject request to MITRE is expected to be slow so that page will remains showing the outdated data for a while longer.

Exploit one

When Apple had retracted the wrong CVE, I figured I should maybe try to get exploitone.com to remove their “article” to maybe at least stop one avenue of further misinformation about this curl “issue”. I tweeted (in perhaps a tad bit inflammatory manner):

I get the feeling they didn’t quite understand my point. They replied:

What happened?

As I had questions about Apple’s mishap, I replied (sent off 22:28 on the 21st, still only early afternoon on the US west coast), asking for details on what exactly had happened here. If it was a typo, then how come it got registered with MITRE? It’s just so puzzling and mysterious!

When I’m posting this article on my blog (36 hours after I sent the question), I still haven’t gotten any response or explanation. I don’t expect to get any either, but if I do, I will update this post accordingly.

Update March 26

exploitone.com updated their page at some point after my tweet to remove the mention of the imaginary CVE, but the wording remains very odd:

Free Apple support

Imagine running a trillion dollar company that bundles various open source components into your products, making billions of dollars of profit annually. When one of your users reach out and ask for help, with the product you ship to your customers, you instead refer the user to the open source project. The project which is run by volunteers which you never sponsored with a cent.

Who would do something like that?

curl’s first twenty years on the mac

September 25, 2001 is the official release date for Mac OS X 10.1. Exactly twenty years ago today.

Mac OS X 10.1

This was the first macOS release from Apple that bundled curl. It was a complete surprise to me as well when I realized this had happened. Nobody had told me about it ahead of time. I don’t even recall anymore how I figured this out, as I’m not a mac user and I’ve never had any direct contact with the peeps at Apple Inc who were and are responsible for shipping curl on that platform. Not before then and not after that either.

The general consensus at the time seemed to be that Apple replaced Wget with curl due to licensing reasons as Wget had been included in their previous OS X release. Wget is licensed under GPL and curl comes under an MIT-like license. I’m not sure if they shipped libcurl too already at that point.

Various Apple products have been using libcurl over the years on several of their operating systems.

We ship source, they build and ship binaries

Apple downloaded our source code tarball, built curl from it and shipped it. (They also made the exact code they used available.) If I remember this correctly, they built curl against OpenSSL and shipped a version of that as well in the beginning.

In later macOS releases (you know they later changed the name of their OS from being Mac OS X to macOS), they’ve switched curl to use different TLS backends over time. At one point they converted over to using Secure Transport (their own native TLS library) only to somewhat later switch again and then to libressl – which is what the current most recent macOS version uses for curl’s default TLS backend.

curl 7.7.2

The original cURL logo

The original curl version they bundled in that first release had been released by us in April earlier that same year. It was our 55th curl release but curl was only a little over three years old at the time. It was a young project and it was just in the beginning phase of what it would become.

Early, not first

Apple was certainly early with shipping curl bundled with their operating system but they were not first. curl was already then provided to several Linux distributions. Apple might’ve been one if the first to ship it by default though.

I remember that it felt awesome and as some sort of recognition and acknowledgement of what we’ve done.

Other operating systems

During the early 2000s lots of operating systems would ultimately one by one start to package and provide curl for their platforms. Linux distributions and BSD flavors of course, but soon the legacy Unixes would also follow. If it wasn’t offered by the primary vendor, third party providers would very soon offer packages,

iOS

The third party license screen in iOS (click on the image shown on the right here for the full resolution version) includes the curl license, showing that Apple use it in iPhones and iPads. I don’t know for what.

Releases

Apple has kept updating curl in their subsequent operating updates and has done a somewhat reasonable job at keeping up with our releases. In their most up-to-date macOS version 11.5.2 (release date: August 11, 2021) they ship curl 7.64.1, released from us on 2019-03-27. Our 181st release. It has twenty-two known vulnerabilities.

This can be compared to Windows 10 which keeps shipping OS updates very frequently but is seemingly stuck with curl 7.55.1, released in August 2017.

Futile attempts to help

For a while I reported security issues we found (that would be relevant) to Apple product security ahead of time before our releases went public, to give them time to react and ship fixes, the same way we send alerts to free operating systems.

I stopped doing that because 1. the Apple security people always complained on me for giving them too short time to react (something like two weeks, which is also the maximum notification time allowed by others) and 2. Apple never released any quick updates as a reaction to my notifications anyway. It took them months or years, making my efforts pointless. Basically they were just rude.

Nothing in return

Neither me personally nor the project have ever gotten anything or any compensation from Apple. Nothing. Nada. Perhaps Apple using curl early on was somewhat of a stamp of approval for some, which helped persuade others that curl is a tool to trust. Perhaps.

Apple has not sponsored the project, not paid for feature development, not helped us with hardware and never paid for support. They don’t cooperate with us to help us fix Apple-specific issues nor do they ever report problems to us (which we know they must find occasionally). Apple users who run into problems with curl on Apple’s operating systems regularly contact the curl project to get us to help fix Apple’s products. For free of course. We never even get a thank you.

I have a mac these days (purchased with my own money) that I use to debug and test mac-specific issues and problems on.

Apple is of course far from alone is this almost predatory behavior, but this post is about curl’s twenty years of serving Apple customers. Also: yes curl is open source and the license allows them to do this. We continue to ship a product that runs perfectly on macOS and other Apple operating systems. They continue to ship curl bundled with their operating systems.

Future

The curl project has no drastic course-altering changes planned ahead and we’re not going away, so I believe the tool and library have the potential to continue being used on Apple products going forward as well. Possibly for a long time ahead. I have zero knowledge or visibility into that, so it’s just guessing on my part based on what’s been done in the past twenty years.

isalnum() is not my friend

The other day we noticed some curl test case failures, that only happened on macos and not on Linux. Curious!

The failures were detected in our unit test 1307, when testing a particular internal pattern matching function (Curl_fnmatch). Both targets run almost identical code but somehow they ended up with different results! Test cases acting differently on different platforms isn’t an extremely rare situation, but in this case it is just a pattern matching function and there’s really nothing timing dependent or anything that I thought could explain different behaviors. It piqued my interest, so I dug in.

The isalnum() return value

Eventually I figured out that the libc function isalnum(), when it got the 8 input value hexadecimal c3 (decimal 195), would return true on the macos machine and false on the box running Linux with glibc!

int value = isalnum(0xc3);

Setting LANG=C before running the test on macos made its isalnum() return false. The input became c3 because the test program has an UTF-8 encoded character in it and the function works on bytes, not “characters”.

Or in the words of the opengroup.org documentation:

The isalnum() function shall test whether c is a character of class alpha or digit in the program’s current locale.

It’s all documented – of course. It was just me not really considering the impact of this.

Avoiding this

I don’t like different behaviors on different platforms given the same input. I don’t like having string functions in curl act differently depending on locale, mostly because curl and libcurl can very well be used with many different locales and I prefer having a stable fixed behavior that we can document and stand by. Also, the libcurl functionality has never been documented to vary due to locale so it would be a surprise (bug!) to users anyway.

We’ve now introduced a private version of isalnum() and the rest of the ctype family of functions for curl. Hopefully this will make the tests more stable now. And make our functions work more similar and independent of locale.

See also: strcasecmp in Turkish.

poll on mac 10.12 is broken

When Mac OS X first launched they did so without an existing poll function. They later added poll() in Mac OS X 10.3, but we quickly discovered that it was broken (it returned a non-zero value when asked to wait for nothing) so in the curl project we added a check in configure for that and subsequently avoided using poll() in all OS X versions to and including Mac OS 10.8 (Darwin 12). The code would instead switch to the alternative solution based on select() for these platforms.

With the release of Mac OS X 10.9 “Mavericks” in October 2013, Apple had fixed their poll() implementation and we’ve built libcurl to use it since with no issues at all. The configure script picks the correct underlying function to use.

Enter macOS 10.12 (yeah, its not called OS X anymore) “Sierra”, released in September 2016. Quickly we discovered that poll() once against did not act like it should and we are back to disabling the use of it in preference to the backup solution using select().

The new error looks similar to the old problem: when there’s nothing to wait for and we ask poll() to wait N milliseconds, the 10.12 version of poll() returns immediately without waiting. Causing busy-loops. The problem has been reported to Apple and its Radar number is 28372390. (There has been no news from them on how they plan to act on this.)

poll() is defined by POSIX and The Single Unix Specification it specifically says:

If none of the defined events have occurred on any selected file descriptor, poll() waits at least timeout milliseconds for an event to occur on any of the selected file descriptors.

We pushed a configure check for this in curl, to be part of the upcoming 7.51.0 release. I’ll also show you a small snippet you can use stand-alone below.

Apple is hardly alone in the broken-poll department. Remember how Windows’ WSApoll is broken?

Here’s a little code snippet that can detect the 10.12 breakage:

#include <poll.h>
#include <stdio.h>
#include <sys/time.h>

int main(void)
{
  struct timeval before, after;
  int rc;
  size_t us;

  gettimeofday(&before, NULL);
  rc = poll(NULL, 0, 500);
  gettimeofday(&after, NULL);

  us = (after.tv_sec - before.tv_sec) * 1000000 +
    (after.tv_usec - before.tv_usec);

  if(us < 400000) {
    puts("poll() is broken");
    return 1;
  }
  else {
    puts("poll() works");
  }
  return 0;
}

Follow-up, January 2017

This poll bug has been confirmed fixed in the macOS 10.12.2 update (released on December 13, 2016), but I’ve found no official mention or statement about this fact.

Changing networks on Mac with Firefox

Not too long ago I blogged about my work to better deal with changing networks while Firefox is running. That job was basically two parts.

A) generic code to handle receiving such a network-changed event and then

B) a platform specific part that was for Windows that detected such a network change and sent the event

Today I’ve landed yet another fix for part B called bug 1079385, which detects network changes for Firefox on Mac OS X.

mac miniI’ve never programmed anything before on the Mac so this was sort of my christening in this environment. I mean, I’ve written countless of POSIX compliant programs including curl and friends that certainly builds and runs on Mac OS just fine, but I never before used the Mac-specific APIs to do things.

I got a mac mini just two weeks ago to work on this. Getting it up, prepared and my first Firefox built from source took all-in-all less than three hours. Learning the details of the mac API world was much more trouble and can’t say that I’m mastering it now either but I did find myself at least figuring out how to detect when IP addresses on the interfaces change and a changed address is a pretty good signal that the network changed somehow.