Date: Tue, 21 Apr 2020 19:47:47 +0100 From: Simon McVittie <smcv@...ian.org> To: oss-security@...ts.openwall.com Cc: "info@...nvakil.com" <info@...nvakil.com> Subject: Re: Pacman package manager - taking untrusted input On Tue, 21 Apr 2020 at 21:51:56 +0430, Amin Vakil wrote: > On 4/21/20 8:57 PM, jellicent@...tonmail.com wrote: > > The code supports database signatures, so the real issue is the distro > > infrastructure. I interpret this as: pacman can accept either signed or unsigned databases, but the various distros that use pacman (such as Arch Linux) currently only publish unsigned databases in practice. Is that correct? Can pacman be configured to *only* accept signed databases, so that a mirror containing an unverifiable database (unsigned, signed with a key that is not explicitly trusted, or with an invalid signature) is treated as an error? If it cannot, then there's an obvious downgrade attack: a malicious mirror could substitute an unsigned database and the pacman client would happily use that. On Tue, 21 Apr 2020 at 17:41:42 +0000, jellicent@...tonmail.com wrote: > An attacker need only find a bug in how Pacman does > parsing/reading of the database file to potentially get code execution > on the box as root. My understanding is that this is a risk, and at least arguably a design flaw, but not generally considered to be a vulnerability (CVE IDs, etc.) unless/until an unfixed parser bug with the necessary severity is found. Of course, that doesn't mean it wouldn't be a good idea to authenticate the database before parsing it: that would mitigate a lot of potential vulnerabilities. Something that might be considered to be a vulnerability already (or not, depending on the pacman and distro maintainers' threat models) is that an attacker could substitute a database that lists obsolete packages with known vulnerabilities. Those packages will presumably be validly signed by distro developers (because at one time they were considered to be the best version available). Presumably pacman won't normally downgrade from the version it has installed to a strictly older version from a mirror, but if a user installs a new (not currently installed) package using that mirror/database, they'll unknowingly be installing an older package that has known vulnerabilities. That form of attack is difficult to address in general, because it needs a revocation or expiry mechanism. apt-based distros are starting to address equivalent issues by setting a Valid-Until field on their archive metadata, so that clients will warn their user if presented with outdated archive metadata (the equivalent of pacman's database) - although this is somewhat awkward to deploy, because it requires a signing key to be made available on a regular basis, which conflicts with the idea that high-value signing keys should be kept offline when not in use. smcv
Powered by blists - more mailing lists
Please check out the Open Source Software Security Wiki, which is counterpart to this mailing list.
Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.