[CVE-2026-74485][MODERATE REGULAR] binfmt_misc: reject a flag character as the field delimiter

[CVE-2026-74485][MODERATE REGULAR] binfmt_misc: reject a flag character as the field delimiter

[AL-KERNEL]

CVE: CVE-2026-74485
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: binfmt_misc: reject a flag character as the field delimiter
Commit: 1819f82dee766c58295ecaacdac02cdf6837d7a4
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1819f82dee766c58295ecaacdac02cdf6837d7a4
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74485
Analysis date: Sat, 15 Aug 2026 16:59:23 -0400
ActionableScore: 3
ActionableScore lower bound: unknown
Actionable bucket: Borderline manual review recommended, not Important by current evidence
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-74485 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74485

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 REGULAR
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-2026-74485	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-125;*CWE-20;CWE-1284;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'binfmt_misc registration can read past the end of an allocated buffer when the user selected field delimiter is also one of the flag characters P O C or F. The flags parser consumes these bytes as valid flags instead of treating the padding as a terminator, so a crafted registration string can drive an out of bounds read beyond the copied user buffer. For the CVSS the PR:L value is used because triggering requires local code execution in a user namespace with access to a binfmt_misc mount, even though no administrator privileges are normally required there. The issue is not network reachable and is triggered through a local filesystem style registration interface. Impact is primarily denial of service because the overread may reach an unmapped page and crash the kernel, while the patch context does not show a write primitive or a direct data disclosure path.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended, not Important by current evidence (with actual score 3)	YES	READ KASAN OOB LOCK DISK LINUS  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	NO	NO	checked

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

ActionableScore=3

1. ActionableScore
* Conservative score: 3
* Paranoid score: 3
* Final recommended bucket: **Borderline manual review recommended, not Important by current evidence**::

2. Signal breakdown
* Local unprivileged trigger: +1. The commit states that binfmt_misc mounts are available to unprivileged users in a user namespace.
* Availability impact realistic: +1. The parser can read beyond the allocation and may reach an unmapped page, causing a kernel crash.
* Broad local namespace exposure: +1. The affected interface is reachable through a local namespace-enabled filesystem registration path, not only host-root administration.
* Limited read-only OOB: +0. This is an out-of-bounds read, but no user-visible information disclosure, write primitive, UAF, double free, or object replacement is shown.
* No LPE bonus. The patch supports DoS risk, but not privilege escalation.

3. Reachability analysis
A local user can trigger the bug by registering a crafted binfmt_misc entry where the delimiter is one of P, O, C, or F. User namespaces can lower the practical privilege requirement because binfmt_misc can be mounted there without full host-root privileges. The path is not network reachable. Exploitation depends on local access and on allocation layout for the crash outcome, but the invalid read itself is directly reachable.

4. Severity interpretation
This behaves like an actionable local Moderate / borderline issue rather than an Important-class vulnerability. The bug is a kernel out-of-bounds read reachable by an unprivileged local user, so it should not be auto-closed without review. Realistic impact is mainly denial of service. Current evidence does not support confidentiality impact, integrity impact, or LPE because there is no leak path, write primitive, UAF reclaim, type confusion, callback control, or refcount abuse.

5. One-sentence report phrase
A local unprivileged user in a user namespace can trigger a binfmt_misc out-of-bounds read by choosing a flag character as the registration delimiter, potentially causing a kernel crash, but no direct data disclosure or privilege escalation primitive is shown.

6. Manual review recommendation
MANUAL CHECK REQUIRED.
Reason: unprivileged local kernel OOB read with possible crash is security-relevant, but current evidence supports DoS only and does not justify Important severity without additional exploitability evidence.

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

Patch: binfmt_misc: reject a flag character as the field delimiter
Commit: 1819f82dee766c58295ecaacdac02cdf6837d7a4
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1819f82dee766c58295ecaacdac02cdf6837d7a4

Commit description:

The registration string starts with a user chosen delimiter that
separates the individual fields. So that the field parsers terminate
even on a truncated string create_entry() pads the buffer with that
same delimiter:

	memset(buf + count, del, 8);

Most fields are scanned for the delimiter with strchr()/scanarg() and
happily stop on the padding. The flags field is different: instead of
scanning for the delimiter check_special_flags() consumes the flag
characters 'P', 'O', 'C' and 'F' and stops at the first byte that is
none of them, relying on the trailing delimiter to end the scan.

If the delimiter is itself a flag character the padding no longer acts
as a terminator. The scan swallows all eight padding bytes and keeps
reading past the end of the allocation until it hits a byte that is
not a flag character. For example registering

	PaPEPPxPPiP

with 'P' as the delimiter (name "a", type extension, magic "x",
interpreter "i", empty flags) leaves the flag scan running off the end
of the buffer. The registration is rejected in the end because the
parser does not stop exactly at buf + count, but only after the out of
bounds read has already happened. With an unlucky allocation layout the
scan can walk into an unmapped page; under KASAN it is reported as a
slab out of bounds read. binfmt_misc mounts are available to
unprivileged users in a user namespace so the read is reachable without
privileges.

Reject a delimiter that is one of the flag characters up front. Such a
registration was always rejected anyway, only after the out of bounds
read, so no valid registration string changes meaning.

Link: https://patch.msgid.link/20260710-work-binfmt_misc-locking-v3-3-a162f7cb58d6@kernel.org
Fixes: 1da177e ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/binfmt_misc.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=1819f82dee766c58295ecaacdac02cdf6837d7a4

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

The original Linux kernel CVE announcement for CVE-2026-74485 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74485

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:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: 3

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 REGULAR

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).