* [CVE-2026-80777][MODERATE 7.0] futex/pi: Plug private futex exec() race
@ 2026-09-04 22:10 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-04 22:10 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-80777
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: futex/pi: Plug private futex exec() race
Commit: fdf538b2e69653ff740e84042245018e5680cd7b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fdf538b2e69653ff740e84042245018e5680cd7b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80777
Analysis date: Fri, 04 Sep 2026 18:10:11 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES
Summary:
A local race in futex PI handling during exec can leave private futex owner checks using an old mm that is being replaced and later freed, creating a UAF candidate with at least DoS impact and requiring manual review for possible privilege escalation.
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ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-80777 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80777
The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.
This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.
The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.
Published priority for this report: MODERATE 7.0
Manual review required: YES
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-80777 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-80777 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';CWE-362;*CWE-416;CWE-367;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race in futex PI handling during exec can expose an inconsistent private futex owner state. The owner task completes robust list cleanup and can be treated as FUTEX_STATE_OK while it still points to the old mm that is about to be replaced and later freed. A concurrent waiter can pass the private futex mm check and attach PI state to an mm context that is no longer stable, making this a use-after-free candidate rather than a simple warning. For the CVSS the PR:L is used because an unprivileged local process can reach futex and exec paths, although reliable triggering depends on winning a narrow race window. The issue is not network reachable. Impact is at least local denial of service via kernel crash and in the paranoid interpretation may allow confidentiality and integrity impact due to UAF style memory corruption, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5) MAYBE READ DISK INIT RACE IMPROVEONLY LINUS KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP - - checked
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ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
ActionableScoreLower=4
## 1. ActionableScore
* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::
## 2. Signal breakdown
Triggered signals:
* Local unprivileged trigger: +1. Futex and exec paths are reachable by ordinary local processes.
* Memory corruption, weak or indirect corruption candidate: +1. The patch prevents a stale or wrong mm association from being used in futex PI state during exec.
* Real lifetime corruption: +1. The old mm is about to be swapped out and eventually freed while futex PI checks may still observe it.
* Broad/default/common subsystem: +1. Futex is a core Linux synchronization mechanism and is normally enabled.
* Availability impact realistic: +1 in paranoid scoring. A stale mm or inconsistent PI state can plausibly lead to kernel crash or serious task synchronization corruption.
Negative signals:
* Hard or unreliable race / special timing required: -1. Exploitation requires hitting the exec window between futex cleanup completion and mm replacement.
Not awarded:
* Remote reachable: +0. No network path.
* Strong LPE plausibility: +0. The patch supports a UAF candidate, but does not show attacker-controlled reclaim, controlled overwrite, callback control, type confusion, or refcount takeover.
* Strong memory corruption primitive: +0. This is treated as weak lifetime corruption rather than a demonstrated strong primitive.
## 3. Reachability analysis
A local unprivileged process can reach the relevant primitives by using futex PI operations and exec. No CAP_SYS_ADMIN or CAP_NET_ADMIN is required for the basic syscall paths. Containers and namespaces generally do not remove futex or exec reachability, so containerized local users may still be relevant depending on kernel sharing and seccomp policy.
The issue is not network reachable. It requires a race between futex PI owner or waiter handling and exec mm replacement. The race window is narrow, but the subsystem is common and the affected state involves mm lifetime and futex PI ownership checks, so it should not be treated as a simple low-risk correctness fix.
Call-site confidence: high. The commit explicitly references attach_to_pi_owner(), private futex mm checks, futex_key, pi_state, and the exec transition window.
## 4. Severity interpretation
This behaves above ordinary Moderate because it involves a local unprivileged race in a core kernel synchronization path with possible stale mm lifetime use. Realistic demonstrated impact is at least local DoS or task/kernel state corruption. Theoretical privilege escalation is plausible enough for manual review, but the patch does not demonstrate a strong exploit primitive such as controlled UAF reclaim or arbitrary write.
Conservative handling is Borderline manual review recommended with score 4. Paranoid handling is Actionable Moderate with score 5 because the bug is a race-lifetime issue in futex PI state and could become more serious if a practical stale-object use path is confirmed.
## 5. One-sentence report phrase
A local race in futex PI handling during exec can leave private futex owner checks using an old mm that is being replaced and later freed, creating a UAF candidate with at least DoS impact and requiring manual review for possible privilege escalation.
## 6. Manual review recommendation
MANUAL CHECK REQUIRED.
Reason: this is a local unprivileged race involving futex PI state and mm lifetime. The currently supported primitive is weak and race-dependent, but the affected objects are security-relevant enough that auto-closing would risk missing a practical LPE path.
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: futex/pi: Plug private futex exec() race
Commit: fdf538b2e69653ff740e84042245018e5680cd7b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fdf538b2e69653ff740e84042245018e5680cd7b
Commit description:
The check for private futexes whether the waiter's mm, which is stored in
the futex_key and copied into the pi_state, is the same as the owner's mm
is not sufficient for exec(). exec() has a gap where the mm check fails to
give the correct answer:
exec()
...
exec_release_mm()
futex_exec_release()
tsk::futex::exit_state = EXITING;
cleanup_robust_list();
1) tsk::futex::exit_state = OK;
...
old_mm = tsk::mm;
2) tsk::mm = ->mm;
Between #1 and #2 the check for the mm is wrong as that mm is about to be
swapped out and eventually freed.
Plug this gap by:
1) Setting tsk::futex::exit_state to FUTEX_STATE_DEAD in
futex_exec_release()
2) Setting tsk::futex::exit_state to FUTEX_STATE_OK after
the mm has been switched.
>>From a futex point of view the task is dead after it finished the robust
list cleanup up to the point where it sets the state to OK again.
Fixes: 80367ad ("futex: Add basic infrastructure for local task local hash")
Signed-off-by: Thomas Gleixner <[email protected]>
Reviewed-by: Kyle Zeng <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Cc: [email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
fs/exec.c
include/linux/futex.h
kernel/futex/core.c
kernel/futex/pi.c
Diff excerpt:
Not included in this email. See the upstream URL for the full patch.
Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fdf538b2e69653ff740e84042245018e5680cd7b
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-80777 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80777
The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.
The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.
This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.
The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.
Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:
Conservative CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
The Best / paranoid CVSS score: 7
The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.
CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.
A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.
Conservative ActionableScore: 4
Paranoid ActionableScore: 5
The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.
For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:
ActionableScore below 5 -> MODERATE REGULAR
ActionableScore 5 or more -> MODERATE 7.0
The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.
There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).
KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.
AL-KERNEL base severity for this report: MODERATE
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): MODERATE 7.0
These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).
Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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