[CVE-2026-63801][MODERATE 7.0] tipc: fix slab-use-after-free Read in tipc_aead_decrypt_done

[CVE-2026-63801][MODERATE 7.0] tipc: fix slab-use-after-free Read in tipc_aead_decrypt_done

[AL-KERNEL]

CVE: CVE-2026-63801
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: tipc: fix slab-use-after-free Read in tipc_aead_decrypt_done
Commit: 171d31245d11bf84836fad3b394cb465a4d008ec
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=171d31245d11bf84836fad3b394cb465a4d008ec
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63801
Analysis date: Sun, 19 Jul 2026 09:56:00 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A confirmed use-after-free read in the TIPC crypto decrypt completion path can occur when async AEAD completion outlives network namespace teardown, allowing a local namespace-capable attacker with TIPC crypto setup to trigger a kernel crash and requiring manual review for possible UAF security impact.

======================================================================
ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-63801 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63801

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-2026-63801	MODERATE	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-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A use-after-free read can occur in the TIPC crypto decrypt path because tipc_aead_decrypt can submit an asynchronous crypto_aead_decrypt request without holding a reference to the network namespace. If the namespace is torn down before the async completion runs, tipc_aead_decrypt_done may dereference freed per-netns tipc_crypto state such as crypto stats, net, aead arrays, and node table data. For the CVSS the PR:L is selected for the paranoid score because reliable triggering may be possible for a local user with namespace or delegated network administration capability rather than requiring full host root. The issue is not a simple unauthenticated Internet remote bug, but crafted encrypted TIPC traffic can participate in the trigger when TIPC crypto and an async AEAD provider are in use. Impact is at least a local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to kernel use-after-free memory corruption. AC:H is used because the bug depends on a race window between asynchronous crypto completion and namespace teardown.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	READ INIT TIPC UAF  KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS	NO	NO	checked

======================================================================
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

Conservative scoring:

* Local unprivileged or namespace-assisted trigger: +1
  The reproducer involves `unshare()` and netns teardown. Reliable triggering likely requires local control of a namespace or delegated network administration capability.
* Memory corruption, weak primitive: +1
  This is a confirmed slab-use-after-free read, but the patch and report show stale reads rather than controlled reclaim, write-after-free, callback hijack, or type confusion.
* Real lifetime corruption: +1
  The bug is an async completion lifetime mismatch. `tipc_aead_decrypt_done()` can outlive `tipc_crypto_stop()` and access freed per-netns crypto state.
* Reliable kernel crash / strong DoS: +1
  KASAN shows a real slab-use-after-free in a worker context. A kernel crash is realistic.
* Availability impact realistic: +1
  The impact is host kernel instability/crash when the race is hit.
* Hard race / special timing: -1
  Triggering requires async AEAD completion to run after namespace teardown.
* Rare or configuration-dependent exposure: -1
  Requires TIPC crypto, a configured bearer/key, and an async AEAD provider path such as cryptd offload.

Conservative total: 4

Paranoid adjustment:

* Do not apply the rare/config penalty fully in paranoid mode because the affected path is packet-driven once TIPC crypto is configured, and the UAF is confirmed by KASAN.
* Race-UAF downgrade rule still applies. No strong LPE primitive is demonstrated.

Paranoid total: 5

## 3. Reachability analysis

The bug is not a simple unauthenticated Internet-remote issue. Crafted encrypted TIPC packets can drive the decrypt path, but the demonstrated trigger also requires teardown of the relevant network namespace while an async crypto completion is pending.

In typical deployments, configuring TIPC bearers and crypto requires administrative or `CAP_NET_ADMIN`-like privileges. However, user namespaces or delegated network namespaces can lower the practical privilege requirement to a local unprivileged user in some environments. This makes `PR:L` a defensible paranoid interpretation.

The path is not broadly default-enabled. It depends on TIPC crypto and an async AEAD implementation. On systems where TIPC crypto is unused or where decrypt completes synchronously, practical exposure is lower.

Call-site confidence: high. The patch directly shows the missing `maybe_get_net()` before `crypto_aead_decrypt()` and the matching `put_net()` in both synchronous and async completion paths.

## 4. Severity interpretation

This behaves more like an actionable Moderate with Important-candidate review than an ordinary Moderate.

Theoretical risk is elevated because this is a real kernel UAF in an asynchronous networking crypto completion path. However, realistic exploitation evidence currently shows stale reads and crash potential, not attacker-controlled reclaim, write-after-free, arbitrary write, object replacement, or callback control. Therefore the conservative score should not treat it as a proven LPE.

The paranoid score is higher because kernel UAF lifetime bugs in network-adjacent async paths are historically worth manual review, especially when namespace delegation may make triggering available to less-privileged local users.

## 5. One-sentence report phrase

A confirmed use-after-free read in the TIPC crypto decrypt completion path can occur when async AEAD completion outlives network namespace teardown, allowing a local namespace-capable attacker with TIPC crypto setup to trigger a kernel crash and requiring manual review for possible UAF security impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: confirmed kernel UAF, async completion lifetime mismatch, packet-driven decrypt path, and possible namespace-assisted local reachability. The demonstrated primitive is mainly DoS, but the bug class and call path are security-relevant enough to avoid auto-closure.

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: tipc: fix slab-use-after-free Read in tipc_aead_decrypt_done
Commit: 171d31245d11bf84836fad3b394cb465a4d008ec
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=171d31245d11bf84836fad3b394cb465a4d008ec

Commit description:

tipc_aead_decrypt() goes straight from tipc_bearer_hold(b) to
crypto_aead_decrypt(req) without taking a reference on the netns, unlike
the encrypt path. When crypto_aead_decrypt() is offloaded asynchronously
(e.g. the SIMD aead wrapper queuing to cryptd), the cryptd worker runs
tipc_aead_decrypt_done() later. If the bearer's netns is torn down in the
meantime, cleanup_net() -> tipc_exit_net() -> tipc_crypto_stop() frees the
per-netns tipc_crypto, and the completion then reads it:
tipc_aead_decrypt_done() dereferences aead->crypto->stats and
aead->crypto->net, and tipc_crypto_rcv_complete() dereferences
aead->crypto->aead[] and the node table -- reading freed memory.

Decoded KASAN splat (v7.1-rc7, CONFIG_KASAN_INLINE + TIPC + TIPC_CRYPTO):

  BUG: KASAN: slab-use-after-free in tipc_aead_decrypt_done (net/tipc/crypto.c:999)
  Read of size 8 at addr ffff8881056258a8 by task kworker/u16:2/51
  Workqueue: events_unbound
  Call Trace:
   tipc_aead_decrypt_done (net/tipc/crypto.c:999)
   process_one_work (kernel/workqueue.c:3314)
   worker_thread (kernel/workqueue.c:3397 kernel/workqueue.c:3478)
   kthread (kernel/kthread.c:436)
   ret_from_fork (arch/x86/kernel/process.c:158)
   ret_from_fork_asm (arch/x86/entry/entry_64.S:245)

  Allocated by task 169:
   __kasan_kmalloc (mm/kasan/common.c:398 mm/kasan/common.c:415)
   tipc_crypto_start (net/tipc/crypto.c:1502)
   tipc_init_net (net/tipc/core.c:72)
   ops_init (net/core/net_namespace.c:137)
   setup_net (net/core/net_namespace.c:446)
   copy_net_ns (net/core/net_namespace.c:579)
   create_new_namespaces (kernel/nsproxy.c:132)
   __x64_sys_unshare (kernel/fork.c:3316)
   do_syscall_64 (arch/x86/entry/syscall_64.c:63)
   entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)

  Freed by task 8:
   kfree (mm/slub.c:6566)
   tipc_exit_net (net/tipc/core.c:119)
   cleanup_net (net/core/net_namespace.c:704)
   process_one_work (kernel/workqueue.c:3314)
   kthread (kernel/kthread.c:436)

This is the same class of bug that commit e279024 ("net/tipc: fix
slab-use-after-free Read in tipc_aead_encrypt_done") fixed for the encrypt
side. The encrypt path takes maybe_get_net(aead->crypto->net) before
crypto_aead_encrypt() and drops it with put_net() on the synchronous
return paths and in tipc_aead_encrypt_done(); the -EINPROGRESS/-EBUSY
return keeps the reference for the async callback to release. The decrypt
path was left without the equivalent guard.

Mirror the encrypt-side fix on the decrypt path: take a net reference
before crypto_aead_decrypt() (failing with -ENODEV and the matching
bearer put if it cannot be acquired), keep it across the
-EINPROGRESS/-EBUSY async return, and drop it with put_net() on the
synchronous success/error return and at the end of
tipc_aead_decrypt_done().

Reproduced under KASAN on v7.1-rc7: a UDP bearer with a cluster key is
flooded with crafted encrypted frames from an unknown peer (driving the
cluster-key decrypt path) while the bearer's netns is repeatedly torn
down. The completion must run asynchronously to outlive
tipc_crypto_stop(); on x86 the stock aesni gcm(aes) now decrypts
synchronously, so the async path was exercised via cryptd offload. The
unguarded aead->crypto dereference in tipc_aead_decrypt_done() is the
unpatched upstream path; tipc_aead_decrypt() still lacks
maybe_get_net(aead->crypto->net), so the completion can outlive the free
on any config where crypto_aead_decrypt() goes async.

Found by 0sec automated security-research tooling ( https://0sec.ai ).

Fixes: fc1b6d6 ("tipc: introduce TIPC encryption & authentication")
Cc: stable@vger.kernel.org
Signed-off-by: Doruk Tan Ozturk <doruk@0sec.ai>
Reviewed-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Reviewed-by: Tung Nguyen <tung.quang.nguyen@est.tech>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20260617075818.37431-1-doruk@0sec.ai
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/tipc/crypto.c
  kernel/workqueue.c
  kernel/kthread.c
  arch/x86/kernel/process.c
  arch/x86/entry/entry_64.S
  mm/kasan/common.c
  net/tipc/core.c
  net/core/net_namespace.c
  kernel/nsproxy.c
  kernel/fork.c
  arch/x86/entry/syscall_64.c
  mm/slub.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=171d31245d11bf84836fad3b394cb465a4d008ec

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-63801 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63801

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.
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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).