Date: Tue, 14 Mar 2023 16:57:25 -0400 From: Shawn Webb <shawn.webb@...denedbsd.org> To: oss-security@...ts.openwall.com Subject: Re: TTY pushback vulnerabilities / TIOCSTI On Tue, Mar 14, 2023 at 09:51:03AM +0100, Hanno Böck wrote: > Hi, > > This blogpost highlights TTY Pushback vulnerabilities enabled via the > TIOCSTI kernel functionality available in the Linux kernel: > https://www.errno.fr/TTYPushback.html > > This has been discussed here previously: > https://www.openwall.com/lists/oss-security/2017/06/03/9 > > Though I think there are some noteworthy updates. In the 2017 post > solar designer mentioned that the Linux kernel developers have multiple > times rejected changes in the kernel. However this has now changed: > Starting with Kernel 6.2 it is possible to disable TIOCSTI > (unset CONFIG_LEGACY_TIOCSTI). It also appears that very few (or no?) > applications practically use TIOCSTI. > > This seems to be the only real mitigation for this issue. It appears > su has a parameter, and in sudo one can configure the creation of a new > pty in the sudoers file. I don't consider these as satisfying fixes, as > they are optinal, and thus rely on the expectation that users are aware > of this risk and manually use these mitigations. That does not seem > realistic to me. > > This also affects such a large number of tools, not just > su/sudo-like tools, but also sandboxing tools. E.g. bubblewrap  is > affected by this by default. > > Thus I strongly recommend that people disable this in the kernel. > >  https://github.com/containers/bubblewrap/issues/555 With commit c7d6d4bb4874720d9dab1625df62c2ea6eeb9df5, I've added a toggle in HardenedBSD to disable TIOCSTI. The toggle is set to prohibit TIOCSTI by default. Now attempts to use TIOCSTI will be met with EPERM. I've verified the toggle in a real-world scenario with the doas issue PoC found at . : https://git.hardenedbsd.org/hardenedbsd/HardenedBSD/-/commit/c7d6d4bb4874720d9dab1625df62c2ea6eeb9df5 : https://github.com/Duncaen/OpenDoas/issues/106#issuecomment-1467202981 Thanks, -- Shawn Webb Cofounder / Security Engineer HardenedBSD https://git.hardenedbsd.org/hardenedbsd/pubkeys/-/raw/master/Shawn_Webb/03A4CBEBB82EA5A67D9F3853FF2E67A277F8E1FA.pub.asc Download attachment "signature.asc" of type "application/pgp-signature" (834 bytes)
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