* [CVE-2026-80850][IMPORTANT] tcp: fix AO info use-after-free in tcp_ao_connect_init()
@ 2026-09-04 19:40 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-04 19:40 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-80850
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: tcp: fix AO info use-after-free in tcp_ao_connect_init()
Commit: 594ba77210a1f065832211851a2d7e14d11fcbdb
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=594ba77210a1f065832211851a2d7e14d11fcbdb
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80850
Analysis date: Fri, 04 Sep 2026 15:40:48 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-80850 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80850
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: IMPORTANT
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-2026-80850 IMPORTANT https://www.kernelcve.org/list/?q=CVE-2026-80850 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-416;CWE-362;CWE-667;BEST CVSS score: '7';DESCR 'A race in TCP_AO connection setup can free tcp ao_info while the receive path still holds an RCU loaded pointer to the old object. The bug is triggered when connect races with detaching the bound device from its VRF while TCP_AO segments are received, causing tcp_inbound_ao_hash to write into freed kernel memory. For the CVSS the PR:L is used because the demonstrated trigger uses an unprivileged local process with self created user and network namespaces to configure TCP_AO, change VRF membership, and race connect with inbound AO traffic. The issue is not a pure remote network bug because local namespace and device control are needed for reliable triggering. Impact is at least local denial of service via kernel crash and may include privilege escalation because KASAN reports a write to a freed kernel object.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate (with actual score 7) SKIP CVE-2026-80850 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE REMOTE OOB DANGER RACE UAF NETWORK HARDWARE KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=7
ActionableScoreLower=6
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=NO
NamespaceScopedPrivilege=YES
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
1. ActionableScore
* Raw conservative score: 6
* Conservative score: 6. No floor or cap changed the score.
* Raw paranoid score: 7
* Paranoid score: 7. No floor or cap changed the score.
* Final recommended bucket: **Strong Important candidate**::
2. Signal breakdown
Conservative positive signals:
* +2 Real UAF / active lifetime violation. tp->ao_info is directly freed with kfree while the receive path may already have loaded the old pointer under RCU and may continue into tcp_inbound_ao_hash.
* +1 Reliable kernel crash / strong DoS. KASAN reports slab-use-after-free in tcp_inbound_ao_hash, and the old WARN_ON_ONCE could also become fatal on panic_on_warn kernels.
* +1 Local unprivileged trigger. The supplied evidence states that an unprivileged reproducer in self-created user and network namespaces triggered the UAF.
* +1 Attacker-influenced active-object lifetime manipulation. The same attacker can repeatedly race connect, VRF detach, and inbound TCP-AO traffic to drive the vulnerable lifetime transition.
* +1 Structured stale-object exploitation leverage. The stale object is active TCP-AO state, and the stale receive path writes to a field inside the freed tcp_ao_info object rather than only performing an immediate NULL dereference or shallow cleanup fault.
Paranoid additional signal:
* +1 Common networking packet-processing path. The stale use occurs from tcp_v4_rcv through tcp_inbound_hash into tcp_inbound_ao_hash, so attacker-controlled packets participate in the vulnerable receive-side processing once TCP-AO is configured.
Important non-awarded signals:
* +0 Remote reachable / directly network-triggerable. Not awarded because the complete reliable trigger requires local namespace and VRF/device control, not just packets from the network.
* +0 Strong LPE / strong exploitation leverage. Not awarded because controlled reclaim, arbitrary write, callback control, credential modification, or demonstrated LPE is not established.
* +0 Confidentiality and integrity bonuses. Not awarded as separate ActionableScore bonuses because no concrete disclosure, arbitrary write, or demonstrated unauthorized state modification beyond the UAF write is shown.
* +0 Extra availability. Not awarded because the same crash/Oops is already counted once.
* 0 race penalty. Not subtracted because the race is repeatable, attacker-driven, and the reproducer reached the vulnerable no-key path hundreds of times per 1000 attempts.
* 0 host-admin penalty. Not subtracted because below-host-admin reachability is positively supplied.
* 0 rare subsystem penalty. Not subtracted because TCP-AO configuration is part of the demonstrated namespace reproducer and not merely a hypothetical host-only deployment condition.
Concrete repeated release/refcount analysis:
* First release can end lifetime: yes, the no-key path directly kfree()s ao_info.
* Exact same reference survives: stale RCU readers can retain the old tp->ao_info pointer loaded before the free.
* Second operation is a real lifetime/refcount mutation: no concrete second put/free/refcount operation on the same object is shown.
* +1 Concrete repeated release/refcount awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 applied: not needed, because arithmetic already exceeds 5. The floor would also be supportable due to a real active-object UAF with below-host-admin reachability and stale structured receive-side processing.
3. Reachability analysis
The evaluated attacker is a local unprivileged user who can create user and network namespaces. The supplied reproducer is described as unprivileged and self-created the user and network namespaces, then raced connect with detaching a veth from its VRF while sending TCP-AO segments.
HostAdminRequired=NO because the supplied evidence positively establishes below-host-admin triggering. NamespaceScopedPrivilege=YES because the complete demonstrated trigger is described as working inside attacker-created user and network namespaces, including TCP-AO setup, VRF membership manipulation, connect, and packet delivery.
The bug is not scored as a pure remote network issue. Packets are part of the trigger, but reliable exploitation requires local control over the socket setup and VRF membership race. No special physical hardware is required. The race is not treated as a hard one-shot race because the attacker can repeatedly attempt it and the supplied statistics show many successful reaches of the vulnerable no-key path.
4. Primitive and severity interpretation
The exact primitive is an RCU lifetime violation causing use-after-free of struct tcp_ao_info. The vulnerable path directly unpublishes tp->ao_info and frees ao_info with kfree, while the receive path may have already loaded the old pointer under RCU and later writes into the freed object in tcp_inbound_ao_hash.
This is active structured object use rather than fixed stale storage. The stale object contains TCP-AO state used by packet validation and counters, and the demonstrated stale operation is a write of size 8 into the freed 128-byte object. The demonstrated consequence is kernel memory corruption with crash potential. The speculative consequence is local privilege escalation, but controlled reclaim or a complete LPE chain is not established.
PrimitiveClass=CLASS_B because this is a real active-object UAF with post-free write, but not a proven Class A primitive such as controlled reclaim, arbitrary kernel write, callback hijack, or demonstrated privilege escalation.
ImportantCandidate=YES because an unprivileged namespace-reachable active-object UAF with a write into freed kernel memory has meaningful unresolved exploitation leverage beyond ordinary crash-only cleanup behavior. AutoDowngradeAllowed=NO because automatic closure would discard a concrete kernel lifetime/corruption primitive that requires manual Important-vs-Moderate review.
Likely operational severity is Actionable Moderate at minimum and a Strong Important candidate for kernel triage.
5. One-sentence report phrase
A race in TCP-AO connection setup can free tcp_ao_info while the receive path still uses an RCU loaded pointer, allowing an unprivileged namespace local attacker to trigger a slab use-after-free write in tcp_inbound_ao_hash and potentially cause a kernel crash or further memory corruption.
6. Manual review recommendation
MANUAL CHECK REQUIRED
This is required because the supplied evidence establishes a real active-object UAF with a write into freed kernel memory, below-host-admin reachability, repeatable attacker-controlled lifetime racing, and unresolved privilege-escalation potential.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: tcp: fix AO info use-after-free in tcp_ao_connect_init()
Commit: 594ba77210a1f065832211851a2d7e14d11fcbdb
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=594ba77210a1f065832211851a2d7e14d11fcbdb
Commit description:
tcp_v4_connect() adds a SYN-SENT socket to the ehash before calling
tcp_connect(). If TCP-AO is configured, tcp_connect() first verifies that
a key matches the peer and the bound device's current L3 master.
tcp_ao_connect_init() later resolves the L3 master again and removes keys
which do not match it.
The socket lock does not stabilize the bound device's VRF membership.
Detaching the device from its VRF between the initial validation and the
L3-master calculation in tcp_ao_connect_init() can therefore make the
validation succeed while initialization observes the default L3 domain and
removes the only key. The subsequent AO lookup then fails, so the no-key
path clears tp->ao_info and frees it directly.
The receive path can find the socket in the ehash and load tp->ao_info
under RCU before acquiring the socket lock. A reader which loaded the old
pointer can thus continue into tcp_inbound_ao_hash() after the direct free.
The issue was found during a static audit of TCP-AO object lifetime. An
unprivileged reproducer in self-created user and network namespaces raced
connect() with detaching a veth from its VRF while sending TCP-AO segments.
It triggered the same KASAN report on two fresh boots:
BUG: KASAN: slab-use-after-free in tcp_inbound_ao_hash+0x585/0x19f0
Write of size 8 at addr ffff88800bf88128 by task tcp_ao_vrf_race/232
Call Trace:
tcp_inbound_ao_hash+0x585/0x19f0
tcp_inbound_hash+0x677/0xa80
tcp_v4_rcv+0x1c3e/0x3ab0
Allocated by task 235:
tcp_ao_alloc_info+0x43/0xf0
tcp_ao_add_cmd+0xdf7/0x13b0
do_tcp_setsockopt+0x168c/0x2640
Freed by task 235:
kfree+0x1b8/0x550
tcp_connect+0x252/0x4f00
tcp_v4_connect+0x1114/0x1720
The bad address is 40 bytes inside the freed 128-byte object, matching the
tcp_ao_info counters.key_not_found field. The two runs used 1000 attempts
each, reached the no-key path 366 and 411 times, and produced one and two
KASAN reports respectively. With this change, the same reproducer reached
the no-key path 366 times in 1000 attempts without a KASAN report or oops.
Use tcp_ao_destroy_sock() for the no-key path. It unpublishes the AO info,
updates the socket memory and static-key accounting, and defers the free
until after an RCU grace period.
Also drop the WARN_ON_ONCE() and its stale comment. The VRF detach race
makes the no-key state reachable during normal operation, so it is a
handled condition rather than an impossible assertion. On panic_on_warn
kernels the WARN would turn this handled race into a kernel panic.
Fixes: 248411b ("net/tcp: Wire up l3index to TCP-AO")
Cc: [email protected]
Assisted-by: Codex:gpt-5
Signed-off-by: Qing Ming <[email protected]>
Reviewed-by: Eric Dumazet <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Paolo Abeni <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
net/ipv4/tcp_ao.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=594ba77210a1f065832211851a2d7e14d11fcbdb
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-80850 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80850
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: Not available
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: 6
Paranoid ActionableScore: 7
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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT
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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