Hello everyone, I've done some small updates to the proposal, mostly improving readability and making my suggestion more clear.
v2 below: I would like to propose something which will lower the amount of reported false-positive CVEs to our users by about 20%. # tl;dr We don't have a unique way of stating that a CVE does not affect us when we don't build the affected package's feature or hardening blocks exploits. This leads to our users being required to manually distinguish which CVEs affect them and which don't. I propose we mark those cases as not-affected. Alternatively, I mention an option to create a new state to indicate that the resulting package is not affected due to the build options. I also explain why that's not my prefered approach. # Problem statement The possible outcomes of a CVE assessment in our security-tracker are[0]: > <no-dsa> | <unfixed> | <undetermined> | <not-affected> | <itp> | <ignored> | > <postponed> We also have the following severity levels [0]: > SEVERITY_LEVEL : (unimportant) | (low) | (medium) | (high) "unimportant" being defined as: > unimportant: This problem does not affect the Debian binary package, e.g., a > vulnerable source file, which is not built, a vulnerable file in > doc/foo/examples/, PHP Safe mode bugs, path disclosure (doesn't matter on > Debian). All "non-issues in practice" fall also into this category, like > issues only "exploitable" if the code in question is setuid root, exploits > which only work if someone already has administrative privileges or similar. > This severity is also used for vulnerabilities in packages which are not > covered by security support. We have a problem in the way we assess CVEs when the generated package is not affected (but the source code contains the vulnerability). Our current process is to set "no-dsa" and lower the severity to "unimportant", although it's also possible that in some cases people are making use of "ignored", which represents "won't fix". The result is that "unimportant/no-dsa" CVEs can mean two things: 1) We are affected but we the severity is too low, eg.: packages not covered by security support, the CVE is considered a non-issue by our security-team but we are still affected... 2) We are definitely not affected since we don't build that feature of the software or we have hardening in place which prevents this from being exploited. This leads to our users, who are interested in knowing which CVEs affect their systems, having to check the notes of every CVE on security-tracker to filter-out the false-positives. # Proposed solution I propose that we start setting CVEs to not-affected also when the following is true for all officially supported architectures: * We don't ship the affected source package. * We don't build the affected feature. * We have hardening which makes the exploit impossible (only in the cases when there's no doubt about it). If we still want to flag the cases where a build with different flags might change that assertion, we can use the "(free text comment)" section of the NOTES[0] to mention it. Effectively this proposal means I would push an MR updating the documentation at [0] and start changing those CVEs to not-affected. I'm not asking for anyone to do the work. # Stats As a way of sampling the impact of this issue, I've done a high-level check on how many sets of affected package-CVE we have in our debian:stable docker image[1]. Out of the 82 affected package/CVE pairs, 15 were clear cases of our packages not being affected. Out of the rest of those, the majority are other cases where we are reporting non-issues, but those require a deeper investigation so I don't want to assume they also fall under this case. So 18% of the reported affected packages are false-positives. Based on what I've seen, I believe this is a fair estimate to extrapolate. I've listed some examples to this issue at [2]. # Alternative solution If using the "free text comment"[0] is not a good enough way of stating that only the source contains the vulnerable code: ## A1) Add a new sub-state "only-source-vulnerable", to be used in addition to "not-affected" ## A2) Add a new mutually exclusive state to the set: "not-affected-build-artifacts" I don't like these approaches because they increase the complexity of our process (a new state is more costly than a free text mention) where there's not a clear benefit/motivation. What's the value in saying the sources carry the vulnerable code? If someone does their own modified build of a package, all bets are off and that's not an official package. It should also be mentioned that identifying cases where only the source-code is vulnerable will never be done perfectly due to how easy it is to miss a bundled library which is not used. For example, rsync bundles zlib and we do not set rsync as affected for all zlib CVEs (rsync does not use the bundled lib), would we like otherwise to be the case? Coming up with a new state is confusing as systems/people reading that might end up parsing it as "affected". So I prefer A1 over A2. This being said, the non-preferred alternatives are still better than the current situation IMHO. [0] https://security-team.debian.org/security_tracker.html#summary-of-tracker-syntax "ignored" and "postponed" are sub-states, supposed to be used together with "no-dsa". [1] $ grype debian:stable [2] https://security-tracker.debian.org/tracker/CVE-2011-3374 [2] https://security-tracker.debian.org/tracker/CVE-2022-0563 [2] https://security-tracker.debian.org/tracker/CVE-2017-18018 [2] https://security-tracker.debian.org/tracker/CVE-2019-19882 [2] https://security-tracker.debian.org/tracker/CVE-2023-28320 Cheers, -- Samuel Henrique <samueloph>
