* [CVE-2026-80860][MODERATE 7.0] fuse: fix race between interrupt and resend
@ 2026-09-04 16:45 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-04 16:45 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-80860
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: fuse: fix race between interrupt and resend
Commit: 26fbe4bc3ef3ab0200407681cbef182af5d151de
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=26fbe4bc3ef3ab0200407681cbef182af5d151de
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80860
Analysis date: Fri, 04 Sep 2026 12:45:28 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
A race between FUSE interrupt queuing and request resend can leave `req->intr_entry` linked when `fuse_request_free()` runs, creating a stale list-entry UAF risk that is locally reachable through FUSE and can cause at least a kernel warning or DoS.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-80860 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80860
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
======================================================================
CVE-2026-80860 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-80860 CHECK WITH IMPACT FROM ORIG NN LOW 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-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in FUSE request handling can occur when an interrupt is queued for a request while the same request is being resent. request_wait_answer may observe FR_SENT before fuse_chan_resend clears it and can then queue req intr_entry after the request is no longer in a valid sent state. This can leave intr_entry linked when fuse_request_free runs, triggering a WARN and creating a plausible stale list entry or UAF style lifetime problem. For the CVSS the PR:L is used because triggering requires local code execution with access to FUSE operations, not full administrative privileges. The issue is not network reachable. Impact is at least local denial of service via kernel warning or crash. In the paranoid case the stale linked request object may allow memory corruption effects and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) SKIP CVE-2026-80860 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE DISK INIT WARNONLY RACE LINUS KPANIC INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4 - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
## 1. ActionableScore
* Raw conservative score: 4
* Conservative score: 4
* Raw paranoid score: 5
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
No floor or cap changed the conservative score. No floor or cap changed the paranoid score.
## 2. Signal breakdown
Conservative signals:
* +2 Real UAF / active lifetime violation: the race can leave `req->intr_entry` linked when `fuse_request_free()` runs. If the request is freed while its embedded list node remains on `fiq->interrupts`, the list can retain a stale reference to freed `struct fuse_req`.
* +1 Local below-host-admin reachability: FUSE is normally reachable by local users through `/dev/fuse` and user FUSE mounts when enabled. This supports PR:L style reachability rather than host-admin-only reachability.
* +1 Reliable kernel warning / likely DoS path: the commit directly reports `WARN_ON(!list_empty(&req->intr_entry))` in `fuse_request_free()`. If `panic_on_warn` is enabled this is immediately fatal, and even without it the stale linked list state is a realistic kernel crash / DoS risk.
* 0 Race penalty not awarded: although this is a race, the evidence does not prove a one-shot, externally uncontrollable, or materially unreproducible timing condition. FUSE request and interrupt/resend activity can likely be retried.
Paranoid additional signal:
* +1 Attacker-influenced active-object lifetime manipulation: in the stronger but still defensible interpretation, the same local FUSE actor can repeatedly generate requests, trigger interruption paths, and influence resend/disconnect style transitions, making the stale list-node state more than a single passive cleanup fault.
Important non-awarded signals:
* Controlled reclaim not demonstrated.
* Arbitrary kernel read/write not demonstrated.
* Callback or function-pointer control not demonstrated.
* C/I impact not awarded merely because a freed `fuse_req` may later be reused.
* Structured stale-object leverage not separately awarded beyond the repeatable lifetime manipulation signal.
* Weak LPE not separately awarded for the same UAF fact.
* Concrete repeated release/refcount signal not awarded: the patch does not show a first `put/free` followed by a second lifetime-mutating `put/free` on the exact same reference.
* Extra availability point not awarded because the warning/crash path is already counted once.
* Remote reachability not established.
Repeated-release/refcount checklist:
* First release can end lifetime: not established as a repeated-release pattern.
* Exact same reference survives into second lifetime mutation: not established.
* Second operation is a real lifetime/refcount mutation: not established.
* +1 Concrete repeated release/refcount awarded: no.
* Paranoid repeated-refcount leverage awarded: no.
* FLOOR 5 applied due repeated release/refcount: no.
## 3. Reachability analysis
The plausible attacker is a local user or local process able to use FUSE operations. Full host administrator privileges are not positively required by the supplied evidence because FUSE is a user-facing filesystem mechanism and `/dev/fuse` is commonly available to non-root users through standard FUSE policy.
The complete namespace-scoped capability story is unresolved. The input does not establish that all required stages are performed only through attacker-created namespaces, so `NamespaceScopedPrivilege=UNKNOWN`.
There is no direct network trigger. The vulnerable path is local FUSE request handling, specifically interaction between request interruption and resend.
Prior host setup may exist in practice because `/dev/fuse`, FUSE mounts, and distribution policy determine whether an ordinary user can instantiate the relevant setup. That does not make the bug host-admin-only for scoring because below-host-admin FUSE use is a normal deployment model.
No special hardware is required. The race is timing-dependent, but the supplied context does not prove it is rare or impractical to repeat.
## 4. Primitive and severity interpretation
The exact primitive is a race in FUSE request state transitions. `request_wait_answer()` can observe `FR_SENT`, then `fuse_chan_resend()` can clear `FR_SENT`, and then the interrupt path can still queue `req->intr_entry`. This can leave the embedded interrupt list entry linked when the owning request is freed.
This is best classified as an active structured object lifetime bug, not fixed stale storage. The affected object is `struct fuse_req`, and the stale element is an embedded `list_head` that participates in kernel list traversal.
This is not merely an ordinary stale cleanup dereference. The demonstrated terminal symptom is a `WARN_ON`, but the underlying state is a linked list node whose owner may be freed, which is a real Class B lifetime primitive. However, it is not Class A because controlled reclaim, directed corruption, arbitrary R/W, callback control, or demonstrated LPE are not established.
Demonstrated consequence: kernel warning and likely local DoS / crash risk.
Speculative consequence: memory corruption or privilege escalation may be possible if the stale list entry can be combined with controlled reclaim or useful post-free object reuse, but that is not proven by the patch.
`ImportantCandidate=YES` because a below-host-admin reachable active-object lifetime violation with a stale linked list entry leaves meaningful exploitation leverage unresolved.
`AutoDowngradeAllowed=NO` because automatically closing this as ordinary Moderate would discard an unresolved concrete kernel lifetime/corruption primitive. The score remains 5 rather than 7 because no strong exploitation primitive is demonstrated.
Likely operational severity: actionable Moderate, with Important review required.
## 5. One-sentence report phrase
A race between FUSE interrupt queuing and request resend can leave `req->intr_entry` linked when `fuse_request_free()` runs, creating a stale list-entry UAF risk that is locally reachable through FUSE and can cause at least a kernel warning or DoS.
## 6. Manual review recommendation
MANUAL CHECK REQUIRED
Reason: this is a real active-object lifetime/list corruption primitive reachable below host-admin in common FUSE deployments, and exploitation leverage beyond crash is unresolved.
## 7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: fuse: fix race between interrupt and resend
Commit: 26fbe4bc3ef3ab0200407681cbef182af5d151de
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=26fbe4bc3ef3ab0200407681cbef182af5d151de
Commit description:
After commit f8fce75 ("fuse: clear intr_entry in fuse_resend and
fuse_remove_pending_req") the WARN_ON(!list_empty(&req->intr_entry)) in
fuse_request_free() still triggers due to the following race:
In request_wait_answer()
if (test_bit(FR_SENT, &req->flags)) -> returns true
In fuse_chan_resend()
clear_bit(FR_SENT, &req->flags)
In request_wait_answer()
queue_interrupt(req)
Fix by:
- move clearing FR_SENT inside fpq->lock
- move setting FR_PENDING inside fiq->lock
- recheck FR_SENT after acquiring fiq->lock in fuse_dev_queue_interrupt()
Reported-by: [email protected]
Fixes: f8fce75 ("fuse: clear intr_entry in fuse_resend and fuse_remove_pending_req")
Cc: [email protected] # 6.9
Signed-off-by: Miklos Szeredi <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
fs/fuse/dev.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=26fbe4bc3ef3ab0200407681cbef182af5d151de
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-80860 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80860
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:N/I:N/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.
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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
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