* [CVE-2026-80890][MODERATE 7.0] sctp: reject stale cookies with mismatched verification tags
@ 2026-09-04 19:16 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-04 19:16 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-80890
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: sctp: reject stale cookies with mismatched verification tags
Commit: f6e3cc296372accad4ee57405195021231ef4bcb
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f6e3cc296372accad4ee57405195021231ef4bcb
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80890
Analysis date: Fri, 04 Sep 2026 15:16:45 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate
Manual review required: NO
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-80890 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80890
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: NO
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-80890 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-80890 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:H';CWE-613;CWE-294;CWE-345;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H';BEST CVSS score: '7.4';DESCR 'SCTP cookie unpacking could accept an expired restart State Cookie when an association already existed even if the cookie Verification Tags did not match the current association. A remote peer with a stale cookie could replay it after expiration and cause COOKIE ACK generation and association restart, which can disrupt an existing SCTP association. For the CVSS the PR:N is selected because no local account or authenticated user context is required on the victim, only network reachability to the SCTP endpoint and a usable stale cookie. The issue is network reachable but the attack complexity is high because the attacker needs a suitable stale cookie and the correct association state. Impact is mainly denial of service through association restart and service disruption, with possible high integrity impact in the paranoid interpretation because protocol state can be changed by an expired replayed cookie.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate (with actual score 5) SKIP CVE-2026-80890 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE INIT SIMPLEFIX NETWORK SKB LINUS TEST KPANIC PACKET - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=NO
1. ActionableScore
* Raw conservative score: 5
* Conservative score: 5. No floor or cap applied.
* Raw paranoid score: 5
* Paranoid score: 5. No additional paranoid point is awarded because no memory corruption, UAF, controlled reclaim, authorization bypass to protected resources, or privilege escalation primitive is established.
* Final recommended bucket: **Actionable Moderate**::
2. Signal breakdown
Positive signals:
* +2 Remote reachable / directly network-triggerable: SCTP packet processing can accept a replayed expired State Cookie from a remote peer reaching the SCTP endpoint.
* +1 Availability impact: replaying the stale restart cookie can restart or disrupt an existing SCTP association.
* +1 Integrity plausible: the bug permits unauthorized protocol state change by accepting an expired cookie that should be rejected when Verification Tags do not match.
* +1 Practical exploit chain demonstrated or strongly implied: the commit describes a runtime test where replaying the cookie after expiration returned COOKIE-ACK and restarted the association.
Negative signals:
* 0 No host-admin penalty: the supplied evidence supports a remote packet trigger and does not require local host-admin privileges.
* 0 No race or timing penalty: the attack requires a suitable stale cookie and association state, but the bug is not a narrow kernel race.
* 0 No rare subsystem penalty: SCTP is optional and less common than TCP, but the vulnerable path is reachable when SCTP service is exposed. Niche deployment alone is not a concrete negative signal.
Important non-awarded signals:
* Memory corruption not awarded because the patch establishes protocol expiration validation failure, not UAF, OOB, refcount misuse, or stale kernel object use.
* RealUAF=NO because no post-lifetime kernel object access is shown.
* Controlled reclaim not demonstrated.
* Arbitrary or directed kernel write not demonstrated.
* Kernel crash not demonstrated.
* Confidentiality impact not awarded because no data disclosure or protected-object read path is established.
* Strong LPE or strong exploitation leverage not awarded because the primitive is replay-driven association state manipulation, not controlled kernel corruption.
* Extra Availability not awarded because the same association restart/disruption is already counted once.
* ImportantCandidate=NO because this is a network protocol logic/replay issue with DoS and protocol integrity impact, but no Important-grade primitive is established.
3. Reachability analysis
The evaluated attacker is a remote SCTP peer or network attacker able to send a previously obtained stale State Cookie to the victim SCTP endpoint. No local account on the victim is required. HostAdminRequired=NO because the trigger is network packet processing against an exposed SCTP association, not a local privileged configuration path.
The attack is not namespace-scoped in the relevant sense. No namespace capability is needed for the remote attacker, and no evidence is supplied that the issue depends on attacker-created network namespaces.
The main practical prerequisite is possession of a usable stale cookie and the correct association state. This raises CVSS-style attack complexity, but it is not a kernel timing race. Prior privileged setup is not part of the exploit path, except that an SCTP service or endpoint must already be present and reachable.
4. Primitive and severity interpretation
The exact primitive is stale State Cookie replay due to overly broad skipping of cookie expiration checks when an association already exists. RFC 9260 permits the expired-cookie exception only when both Verification Tags match the current association. The old condition skipped expiration for any existing association, allowing an expired Action A restart cookie with mismatched tags to reach duplicate-cookie handling and restart the association.
This is not active structured UAF and not fixed stale storage. It is a protocol logic and replay validation flaw. There is no concrete repeated release/refcount operation.
PrimitiveClass=CLASS_C because the demonstrated behavior is invalid protocol state acceptance and association disruption, without a kernel memory corruption primitive. The demonstrated consequence is remote association restart and service disruption. The speculative consequence is broader application-level disruption depending on how SCTP is used, but no kernel LPE, arbitrary write, disclosure, or crash is supported by this patch.
ImportantCandidate=NO because the evidence does not establish Class A or strong Class B leverage. AutoDowngradeAllowed=NO because the issue is remotely reachable and changes protocol state through replay of an expired authentication/state cookie, so it should not be automatically closed as an ordinary low-risk cleanup issue.
Likely operational severity: Actionable Moderate. It is relevant for exposed SCTP deployments and should receive manual protocol/security review, but it is not a strong Important candidate from the supplied evidence.
5. One-sentence report phrase
A remote SCTP peer with a usable stale State Cookie can replay it after expiration and cause COOKIE-ACK generation and association restart when Verification Tags do not match, leading to network reachable denial of service and protocol state integrity impact.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Reason: the issue is network reachable and can alter SCTP association state, but no memory corruption, kernel crash, information disclosure, or privilege escalation primitive is established.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: sctp: reject stale cookies with mismatched verification tags
Commit: f6e3cc296372accad4ee57405195021231ef4bcb
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f6e3cc296372accad4ee57405195021231ef4bcb
Commit description:
sctp_unpack_cookie() skips cookie expiration checks whenever an
association already exists. This is broader than the exception in
RFC 9260 Section 5.2.4.
For an existing association, Section 5.2.4 permits an expired State
Cookie only when both Verification Tags in the cookie match the current
association. Otherwise, the packet SHOULD be discarded and a Stale
Cookie ERROR MUST be sent.
The broad check lets an expired Action A restart cookie reach
sctp_sf_do_dupcook_a(). In a runtime test with the default 60 second
cookie lifetime, replaying such a cookie after 65 seconds returned a
COOKIE-ACK and restarted the association.
Check cookie expiration unless both Verification Tags match. This
preserves the Action D exception for a lost COOKIE ACK while rejecting
expired cookies in all other cases.
Fixes: 1da177e ("Linux-2.6.12-rc2")
Cc: [email protected]
Signed-off-by: Yuxiang Yang <[email protected]>
Acked-by: Xin Long <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
net/sctp/sm_make_chunk.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=f6e3cc296372accad4ee57405195021231ef4bcb
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-80890 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80890
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:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H
The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:H
The Best / paranoid CVSS score: 7.4
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: unknown
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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