On Wed, 2026-08-12 at 02:28 -0500, Junjie Cao wrote: > begin_new_exec() resets dumpability to owner-dumpable whenever the real > and effective ids match at exec time. A binary exec'd by a setuid > program that has already called setuid(0) therefore becomes dumpable as > root, and with a relative core_pattern plus an attacker-controlled > working directory the resulting core file can be dropped into a > privileged directory such as /etc/logrotate.d. > > Full report with proof of concept: > > https://www.openwall.com/lists/oss-security/2021/10/20/2 > > Two fixes were proposed and neither was merged. Waiman Long's patch was > judged an ineffective mitigation by Eric W. Biederman and the discussion > went quiet in early 2022; Wander Lairson Costa's RFC v2 received design > feedback and no v3 followed: > > https://lore.kernel.org/all/[email protected]/ > https://lore.kernel.org/all/[email protected]/ > > The flagged logic is unchanged: fs/exec.c still selects > TASK_DUMPABLE_OWNER in that case, and fs/coredump.c only applies the > suid-safe restriction when dumpable is TASK_DUMPABLE_ROOT, so the > dumpable==1 case this CVE describes is not covered. Images that set an > absolute path, a pipe or a socket core_pattern are not exploitable.
This third paragraph is unnecessary detail. > > CC: Paul Barker <[email protected]> > AI-Generated: Uses Claude (claude-opus-5) > Signed-off-by: Junjie Cao <[email protected]> > --- > v3: > - use "unpatched" instead of "upstream-wontfix"; a NAK of one > mitigation is not an upstream wontfix of the issue > - drop the "NAKed" wording: the discussion went quiet, it was not > formally rejected > > v2: > https://lore.kernel.org/openembedded-core/[email protected]/ > > meta/recipes-kernel/linux/cve-exclusion.inc | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/meta/recipes-kernel/linux/cve-exclusion.inc > b/meta/recipes-kernel/linux/cve-exclusion.inc > index af3576d..ba8e467 100644 > --- a/meta/recipes-kernel/linux/cve-exclusion.inc > +++ b/meta/recipes-kernel/linux/cve-exclusion.inc > @@ -206,3 +206,11 @@ host model, no upstream kernel fix, mitigated by > firewall configuration" > # https://security-tracker.debian.org/tracker/CVE-2021-3714 > CVE_STATUS[CVE-2021-3714] = "unpatched: timing side channel inherent to \ > KSM page deduplication, only reachable when KSM is enabled and opted into" > + > +# Two mitigation attempts, neither merged; the fs/exec.c logic is > +# unchanged. An absolute, piped or socket kernel.core_pattern (for > +# example systemd-coredump) prevents exploitation. > +# https://www.openwall.com/lists/oss-security/2021/10/20/2 > +# https://ubuntu.com/security/CVE-2021-3864 > +CVE_STATUS[CVE-2021-3864] = "unpatched: no accepted mainline fix, \ > +exploitation requires a relative kernel.core_pattern" Suggested wording, links, and include triage date: # Triaged August 2026 - Two fixes proposed upstream but neither was merged, # attempts to fix seem to have petered out. Unfixed in Debian/Ubuntu. # https://lore.kernel.org/all/[email protected]/ # https://lore.kernel.org/all/[email protected]/ # https://security-tracker.debian.org/tracker/CVE-2021-3864 # https://ubuntu.com/security/CVE-2021-3864 CVE_STATUS[CVE-2021-3864] = "unpatched: Proposed fixes were not merged upstream" Best regards, -- Paul Barker
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