[CVE-2026-43078][MODERATE 7.0] crypto: af_alg - Fix page reassignment overflow in af_alg_pull_tsgl

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

CVE: CVE-2026-43078
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: crypto: af_alg - Fix page reassignment overflow in af_alg_pull_tsgl
Commit: fa48d3ea9cdbfb28c1fd6756c6c5cd01351aa51e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fa48d3ea9cdbfb28c1fd6756c6c5cd01351aa51e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43078
Analysis date: Tue, 09 Jun 2026 18:17:48 -0400
ActionableScore: 7
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A local AF_ALG user may trigger an off-by-one scatterlist reassignment in `af_alg_pull_tsgl()`, causing kernel memory corruption or crash, with possible but unproven privilege escalation impact.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-43078 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43078

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-43078	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-193;CWE-682;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.8';DESCR 'AF_ALG page reassignment in af_alg_pull_tsgl can write one scatterlist entry past the expected destination list because the old loop still reassigns a page when plen is zero. A local user that can use AF_ALG sockets may be able to trigger the boundary condition with crafted crypto socket I/O and cause kernel memory corruption or a crash. For the CVSS the PR:L is used because the attacker needs local code execution or a local process context to drive the AF_ALG socket interface, but no administrative privileges are normally required. The issue is not directly network reachable. Impact is at least local denial of service via kernel crash and in the paranoid case may include confidentiality and integrity impact because the bug class is an out-of-bounds write in kernel scatterlist memory.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 6)	YES	DANGER SIMPLEFIX IMPROVEONLY LINUS SYZBOT KPANIC  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	NO	YES	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. AF_ALG sockets are local kernel interfaces normally usable by local processes without full administrative privileges.
* Constrained kernel buffer overwrite: +1. The bug can advance the destination scatterlist index and write one extra `scatterlist` entry, but the written values are mostly kernel-derived page, length, and offset metadata.
* Local unprivileged high-control kernel data-plane API: +1. AF_ALG lets local users shape crypto socket I/O, buffers, and scatterlist processing.
* Reliable kernel crash / strong DoS: +1. A scatterlist overflow in kernel crypto buffer handling is a credible crash path.

Paranoid additional / stronger interpretation:

* Generic memory corruption, strong corruption primitive: +2 instead of constrained +1. The patch context supports an off-by-one OOB write into kernel scatterlist memory.
* Weak LPE concern: +1. No direct privilege escalation primitive is shown, but local kernel OOB write in a high-control AF_ALG path is sufficient for manual LPE review.
* Integrity impact plausible: +1. In the paranoid interpretation, corrupting adjacent kernel scatterlist metadata may affect subsequent kernel data handling.

Not counted:

* Remote reachable: +0. This is not network-triggerable.
* Real lifetime corruption: +0. The patch does not show UAF, double-free, RCU lifetime misuse, or stale callback dispatch.
* Dirty-Pipe-like page-cache primitive: +0. This is not shown to corrupt shared file-backed page cache or bypass COW ownership.

## 3. Reachability analysis

A local user or local process that can create and use AF_ALG sockets may be able to reach `af_alg_pull_tsgl()` through crafted crypto socket I/O. No host root privilege is inherently required for the interface, so PR:L is the practical CVSS-style privilege level.

Containers and sandboxes can matter. If AF_ALG socket creation is allowed inside a container, a containerized unprivileged process may still reach the host kernel code path. Seccomp, LSM policy, disabled modules, or restricted crypto socket families can reduce exposure.

The path is not remotely reachable by packet traffic. It is a local kernel API issue. AF_ALG is not as universal as TCP/IP or VFS, but it is a common kernel crypto interface and should not be treated as rare hardware-only code.

## 4. Severity interpretation

This is stronger than an ordinary Moderate resource leak or validation cleanup because the fix prevents an extra scatterlist reassignment. The direct conservative impact is local DoS through kernel memory corruption or crash.

The realistic exploitation evidence does not demonstrate controlled arbitrary write, attacker-controlled reclaim, callback corruption, or a proven LPE chain. However, the primitive is still an OOB write candidate in a local high-control kernel API. That makes it an Actionable Moderate at minimum and a Strong Important candidate under paranoid triage.

Theoretical memory corruption potential is credible. Practical privilege escalation is not proven from the patch alone, but should not be auto-closed without manual review.

## 5. One-sentence report phrase

A local AF_ALG user may trigger an off-by-one scatterlist reassignment in `af_alg_pull_tsgl()`, causing kernel memory corruption or crash, with possible but unproven privilege escalation impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED.

Reason: the bug is a local kernel OOB write candidate in AF_ALG scatterlist handling. Even though the overwrite appears constrained and no full LPE primitive is demonstrated, this class should receive manual review rather than automatic Moderate closure.

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

Patch: crypto: af_alg - Fix page reassignment overflow in af_alg_pull_tsgl
Commit: fa48d3ea9cdbfb28c1fd6756c6c5cd01351aa51e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fa48d3ea9cdbfb28c1fd6756c6c5cd01351aa51e

Commit description:

When page reassignment was added to af_alg_pull_tsgl the original
loop wasn't updated so it may try to reassign one more page than
necessary.

Add the check to the reassignment so that this does not happen.

Also update the comment which still refers to the obsolete offset
argument.

Reported-by: syzbot+d23888375c2737c17ba5@syzkaller.appspotmail.com
Fixes: e870456 ("crypto: algif_skcipher - overhaul memory management")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  crypto/af_alg.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=fa48d3ea9cdbfb28c1fd6756c6c5cd01351aa51e

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

The original Linux kernel CVE announcement for CVE-2026-43078 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43078

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:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.8

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: 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: 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).