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If you're a developer relying on GnuPG, check upstream for an update that plugs an input sanitisation bug.
The short version, given in CVE-2018-12020, is that mainproc.c mishandles the filename, and as a result, an attacker can spoof the output it sends to other programs.
“For example, the OpenPGP data might represent an original filename that contains line feed characters in conjunction with GOODSIG or VALIDSIG status codes”, the Mitre advisory states.
GnuPG maintainer Werner Koch explained in more detail in this advisory.
The ability to include the input file name in a signed/encrypted message is part of the OpenPGP protocol, so he[sic] recipient can see what file is being decrypted. The bug is that the file name included for display doesn't get sanitised.
As a result, an attacker can include commands in a fake filename, because the filename “may include line feeds or other control characters. This can be used inject terminal control sequences into the out and, worse, to fake the so-called status messages”, Koch's note said.
[...] Koch attributed the discovery to Marcus Brinkmann, and Brinkmann had one complaint about how things were handled, as he wrote to the OSS-sec mailing list: "I tried to disclose this responsibly with Werner Koch (and in coordination with other affected projects), but within two hours he did a unilateral full disclosure without getting back to me."
(Score: 2) by driverless on Wednesday June 13 2018, @12:04PM (4 children)
You have to wonder about a security program that's vulnerable to an attack that's been around since the 1980s. Back then you could upload Zip files with manipulated filenames to a BBS using your 2400 baud modem and cause interesting results based on what you'd done to the filename. Nearly thirty years later, an application specifically written for security is vulnerable to those same issues...
There was an issue from around that time with Zip file comments, anyone checked whether GPG is vulnerable to that one as well?
(Score: 2, Interesting) by Anonymous Coward on Wednesday June 13 2018, @01:37PM (1 child)
This one is actually a completely valid filename that the terminal interprets in a way that causes the problem.
If you're viewing it on anything other than a terminal, it isn't a problem.
If you're viewing it on a hard-copy terminal, the problem is there, but the attempt to abuse it becomes obvious.
Should every program be aware of every weird terminal that was ever made?
(And why are command line programs still using character codes to control a terminal emulator rather than having an API for everything outside text, tab and newline?)
(Score: 0) by Anonymous Coward on Thursday June 14 2018, @12:02AM
This is not quite true, because the filename might still contain newlines and text that looks like gpg status lines. The problem is that some programs run gpg and then parse its output, and they might get confused into thinking a signature verification was successful when, in fact, it was not.
The impact is still pretty low because programs using the library interface are unaffected. The gpgv command is also unaffected.
(Score: 0) by Anonymous Coward on Thursday June 14 2018, @03:44AM (1 child)
To be fair, do you know how many gnupg developers there are? Most people would rather point and laugh instead of doing anything useful.
(Score: 2) by driverless on Thursday June 14 2018, @11:59AM
I only have one doctor, but he still manages to sterilise his instruments before using them, it's just basic hygiene. And that's what this is, basic sanitisation of untrusted input data.
Incidentally, congratulations for outing me as a "M$ sock puppet". Was it the OpenBSD logo on my desktop that gave the game away?