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 "not a particularly effective mitigation" by Eric W. Biederman and the discussion went quiet by 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]/ CC: Paul Barker <[email protected]> AI-Generated: Uses Claude (claude-opus-5) Signed-off-by: Junjie Cao <[email protected]> --- v4: - use the review's comment and status wording; drop the coredump path analysis paragraph - quote Biederman's assessment verbatim v3: 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 36643ccc..36920e2c 100644 --- a/meta/recipes-kernel/linux/cve-exclusion.inc +++ b/meta/recipes-kernel/linux/cve-exclusion.inc @@ -206,3 +206,11 @@ model, no upstream fix" # https://ubuntu.com/security/CVE-2021-3714 CVE_STATUS[CVE-2021-3714] = "unpatched: Timing side channel inherent to Kernel \ Same-page Merging (KSM) page deduplication" + +# 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" -- 2.43.0
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