[CVE-2026-74578][MODERATE 7.0] crypto: algif_skcipher - force synchronous processing on trees without ctx->state The AIO/async path in skcipher_recvmsg() passes the socket-wide ctx->iv directly into the skcipher request. After io_submit() the socket lock is dropped and the request is processed asynchronously, so a concurrent sendmsg(ALG_SET_IV) can overwrite ctx->iv and make the in-flight request run under an attacker-controlled IV. For CTR/stream modes this is IV/keystream reuse and lets an unprivileged user recover the plaintext of a concurrent operation. Snapshotting ctx->iv into per-request storage for the async path is not sufficient. For ciphers with statesize == 0 - which includes cbc and ctr - the MSG_MORE inter-chunk IV chaining is carried solely by the in-place req->iv writeback, which a snapshot redirects into per-request memory that af_alg_free_resources() releases on completion, silently producing wrong output. Writing the IV back from the completion callback instead is not possible either: that would require lock_sock() there, but the callback can run in softirq/atomic context, so it must not sleep. Make the operation synchronous instead, which removes both the IV race and any writeback race. This is equivalent to the upstream resolution,

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-74578
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: crypto: algif_skcipher - force synchronous processing on trees without ctx->state The AIO/async path in skcipher_recvmsg() passes the socket-wide ctx->iv directly into the skcipher request. After io_submit() the socket lock is dropped and the request is processed asynchronously, so a concurrent sendmsg(ALG_SET_IV) can overwrite ctx->iv and make the in-flight request run under an attacker-controlled IV. For CTR/stream modes this is IV/keystream reuse and lets an unprivileged user recover the plaintext of a concurrent operation. Snapshotting ctx->iv into per-request storage for the async path is not sufficient. For ciphers with statesize == 0 - which includes cbc and ctr - the MSG_MORE inter-chunk IV chaining is carried solely by the in-place req->iv writeback, which a snapshot redirects into per-request memory that af_alg_free_resources() releases on completion, silently producing wrong output. Writing the IV back from the completion callback instead is not possible either: that would require lock_sock() there, but the callback can run in softirq/atomic context, so it must not sleep. Make the operation synchronous instead, which removes both the IV race and any writeback race. This is equivalent to the upstream resolution,
Commit: 73dd3bf704ca6c20639de70c08e9a10bee904a95
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=73dd3bf704ca6c20639de70c08e9a10bee904a95
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74578
Analysis date: Sun, 16 Aug 2026 04:53:07 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A local AF_ALG skcipher async race lets an unprivileged process replace the socket-wide IV used by an in-flight request, causing attacker-controlled IV use and possible plaintext recovery in CTR or stream-like modes.

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

The original Linux kernel CVE announcement for CVE-2026-74578 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74578

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-2026-74578	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:N';CWE-362;CWE-323;CWE-329;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:N';BEST CVSS score: '6.3';DESCR 'A race in crypto algif_skcipher allows the async skcipher_recvmsg() path to pass the socket wide ctx iv directly into an in flight skcipher request. After io_submit() the socket lock can be dropped while the request is still processed, so a concurrent sendmsg(ALG_SET_IV) can replace ctx iv and make the operation run with attacker controlled IV material. For CTR and stream like modes this can cause IV or keystream reuse and may allow recovery of plaintext from a concurrent operation. For the CVSS the PR:L is used because triggering requires a local process that can use AF_ALG sockets and submit the racing operations, but no administrative privileges are required in typical configurations. The issue is not network reachable by itself and affects local crypto API users. Impact is mainly confidentiality loss and possible integrity impact through attacker controlled IV selection, not kernel code execution or a direct privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	INIT RACE LOG IMPROVEONLY LINUS IO_URING  DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	guess

======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

* Local unprivileged trigger: +1
  AF_ALG sockets and AIO style requests can be used by a local unprivileged process in typical configurations.

* Local unprivileged high-control kernel data-plane API refinement: +1
  AF_ALG exposes a high-control crypto request API where userspace can shape requests, IV updates, message boundaries, and async behavior.

* Confidentiality impact plausible: +1
  The commit explicitly states that attacker-controlled IV injection in CTR or stream-like modes can cause IV/keystream reuse and plaintext recovery.

* Integrity impact plausible: +1 paranoid only
  Attacker-controlled IV selection can alter cryptographic output semantics. This is not kernel memory corruption, but it is a plausible crypto integrity impact for users of the API.

* Practical exploit chain demonstrated or strongly implied: +1 paranoid only
  The commit reports tested attacker IV injection before the fix and 0 hits after the fix, which strongly supports practical triggerability of the crypto misuse.

* Hard race / special timing required: 0
  The bug is a race, but the provided test data shows repeated successful attacker IV injection, so I would not subtract for an impractical race.

* Legacy / rare mode: 0
  AF_ALG async is said to be rarely used, but AF_ALG is an ordinary local kernel API and the issue is not confined to a rare hardware mode or obscure build-only path.

No memory-corruption, UAF, OOB write, arbitrary write, or direct LPE signal is supported by the patch.

## 3. Reachability analysis

A local process that can open and use AF_ALG skcipher sockets and submit async operations can trigger the issue. No administrative capability is normally required, so PR:L is the right privilege interpretation. The issue is not remotely reachable by itself, because the attacker needs local access to the AF_ALG socket interface and must race `sendmsg(ALG_SET_IV)` against an in-flight async `skcipher_recvmsg()` operation.

Namespaces and containers may matter because AF_ALG availability can expose the same local kernel crypto API inside containerized environments if not restricted by policy. The path is not a common network packet path, but AF_ALG is a real local userspace API and the commit gives evidence that the race was practically observable.

## 4. Severity interpretation

This behaves like an actionable Moderate issue rather than an ordinary Moderate cleanup. It is not a kernel memory corruption or direct privilege escalation bug, but it is a real local crypto race with demonstrated attacker IV injection and plausible plaintext recovery. The conservative interpretation is high confidentiality with limited or uncertain integrity impact. The paranoid interpretation raises the practical triage score because attacker-controlled IV material can affect both confidentiality and integrity of cryptographic operations using CTR or stream-like modes.

It should not be treated as Important solely on kernel-exploitation grounds, because there is no UAF, object replacement, arbitrary write, or privilege escalation primitive. It also should not be auto-closed as low-risk because the impact is not just a crash or warning.

## 5. One-sentence report phrase

A local AF_ALG skcipher async race lets an unprivileged process replace the socket-wide IV used by an in-flight request, causing attacker-controlled IV use and possible plaintext recovery in CTR or stream-like modes.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED.

This is not a memory-safety LPE candidate, but the patch documents a demonstrated crypto race with confidentiality impact and plausible integrity implications, so it should receive manual triage rather than automatic closure.

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

Patch: crypto: algif_skcipher - force synchronous processing on trees without ctx->state The AIO/async path in skcipher_recvmsg() passes the socket-wide ctx->iv directly into the skcipher request. After io_submit() the socket lock is dropped and the request is processed asynchronously, so a concurrent sendmsg(ALG_SET_IV) can overwrite ctx->iv and make the in-flight request run under an attacker-controlled IV. For CTR/stream modes this is IV/keystream reuse and lets an unprivileged user recover the plaintext of a concurrent operation. Snapshotting ctx->iv into per-request storage for the async path is not sufficient. For ciphers with statesize == 0 - which includes cbc and ctr - the MSG_MORE inter-chunk IV chaining is carried solely by the in-place req->iv writeback, which a snapshot redirects into per-request memory that af_alg_free_resources() releases on completion, silently producing wrong output. Writing the IV back from the completion callback instead is not possible either: that would require lock_sock() there, but the callback can run in softirq/atomic context, so it must not sleep. Make the operation synchronous instead, which removes both the IV race and any writeback race. This is equivalent to the upstream resolution,
Commit: 73dd3bf704ca6c20639de70c08e9a10bee904a95
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=73dd3bf704ca6c20639de70c08e9a10bee904a95

Changed files:
  crypto/algif_skcipher.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=73dd3bf704ca6c20639de70c08e9a10bee904a95

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

The original Linux kernel CVE announcement for CVE-2026-74578 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74578

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:H/I:L/A:N
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N
  The Best / paranoid CVSS score: 6.3

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: NO
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).