[CVE-2026-46303][MODERATE REGULAR] isofs: validate Rock Ridge CE continuation extent against volume size

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

CVE: CVE-2026-46303
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: isofs: validate Rock Ridge CE continuation extent against volume size
Commit: 8356fb821016797f5677cbeee5ddc0d32a95b4be
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8356fb821016797f5677cbeee5ddc0d32a95b4be
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46303
Analysis date: Mon, 08 Jun 2026 14:52:03 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
A crafted Rock Ridge ISO image can reference CE continuation blocks outside the mounted ISO volume, creating a narrow local information disclosure path through readlink() when desktop automount or delegated ISO mounting is available.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-46303 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46303

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-2026-46303	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:L/I:N/A:L';*CWE-20;*CWE-200;CWE-668;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '4.4';DESCR 'Rock Ridge CE continuation extent is trusted without checking that the referenced block is inside the ISO 9660 volume. A crafted ISO image can set cont_extent to an out-of-range block or to an in-range block that belongs to adjacent data on the same block device. Out-of-range reads normally fail cleanly through sb_bread and EIO, so this is not a memory corruption issue. The main security concern is a narrow confidentiality exposure where adjacent data may be parsed as Rock Ridge records and limited SL text may become visible through readlink(). For the CVSS the PR:L is used because reliable triggering can be available to a local logged in user when desktop automount or udisks2 permits mounting removable ISO media, while CAP_SYS_ADMIN would be required on more locked down systems. The issue is not network reachable. Impact is mainly limited information disclosure with at most minor availability impact for the malformed mounted filesystem.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 4) 	MAYBE	OOB DISK LEAK HARDWARE LINUS  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline, manual review recommended**::

## 2. Signal breakdown

* Local unprivileged trigger: +1
  A local user may be able to trigger this by providing a crafted ISO image to a desktop automount path such as udisks2. In locked down server deployments, CAP_SYS_ADMIN mount access may be required.

* Filesystem/storage metadata reachable by an unprivileged local user: +1
  The malformed Rock Ridge CE metadata is attacker controlled through the ISO filesystem image.

* Confidentiality impact plausible: +1
  The unchecked cont_extent may point outside the ISO volume but still within the same block device, allowing a narrow possible disclosure path if adjacent data is parsed as Rock Ridge records and exposed through readlink().

* Availability impact realistic, paranoid only: +1
  Out of range reads return EIO cleanly, so no strong DoS is demonstrated. A minor availability impact for the malformed mounted filesystem is plausible but not system wide.

* No memory corruption signal: +0
  The commit explicitly indicates sb_bread() returns NULL cleanly for out of range blocks, and the patch only adds a bounds check against s_nzones.

* No remote/network reachability: +0
  This is a crafted local filesystem image mount path, not a network parser.

## 3. Reachability analysis

A crafted ISO image is required. On desktop systems, a local logged in user may trigger the path through removable media or udisks2 automount, so PR:L is the practical paranoid interpretation. On hardened servers, mounting ISO images usually requires CAP_SYS_ADMIN, which would lower practical exposure. Containers and namespaces may matter only if ISO mounting or a mount helper is delegated into the container. The affected path is not network reachable and depends on ISOFS plus Rock Ridge parsing being used.

## 4. Severity interpretation

This behaves like a low to borderline Moderate information disclosure issue, not an Important kernel memory corruption bug. The realistic impact is a narrow cross-volume read primitive where only data that parses into usable Rock Ridge SL text may reach userspace. There is no evidence of UAF, OOB write, arbitrary write, page-cache corruption, or privilege escalation. Manual review is still reasonable because the bug crosses a filesystem volume boundary and the confidentiality impact depends on block-device layout and automount policy.

## 5. One-sentence report phrase

A crafted Rock Ridge ISO image can reference CE continuation blocks outside the mounted ISO volume, creating a narrow local information disclosure path through readlink() when desktop automount or delegated ISO mounting is available.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the score is low, but the issue has a plausible local confidentiality boundary concern involving adjacent block-device data, so it should not be blindly auto-closed without checking deployment exposure such as udisks2 automount and ISO mounting policy.

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

Patch: isofs: validate Rock Ridge CE continuation extent against volume size
Commit: 8356fb821016797f5677cbeee5ddc0d32a95b4be
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8356fb821016797f5677cbeee5ddc0d32a95b4be

Commit description:

rock_continue() reads rs->cont_extent verbatim from the Rock Ridge CE
record and passes it to sb_bread() without checking that the block
number is within the mounted ISO 9660 volume.  commit e595447
("[PATCH] rock.c: handle corrupted directories") added cont_offset
and cont_size rejection for the CE continuation but did not validate
the extent block number itself.  commit f54e18f ("isofs: Fix
infinite looping over CE entries") later capped the CE chain length
at RR_MAX_CE_ENTRIES = 32 but again left the block number unchecked.

With a crafted ISO mounted via udisks2 (desktop optical auto-mount)
or via CAP_SYS_ADMIN mount, rs->cont_extent can therefore point at
an out-of-range block or at blocks belonging to an adjacent
filesystem on the same block device.  sb_bread() on an out-of-range
block returns NULL cleanly via the block layer EIO path, so there
is no memory-safety violation.  For in-range reads of adjacent-
filesystem data, the CE buffer is parsed as Rock Ridge records and
only the text of SL sub-records reaches userspace through
readlink(), which makes the info-leak channel narrow and difficult
to exploit; still, rejecting the malformed CE outright matches the
rejection shape already present in the same function for
cont_offset and cont_size.

Add an ISOFS_SB(sb)->s_nzones bounds check to rock_continue() next
to the existing offset/size rejection, printing the same
corrupted-directory-entry notice.

Fixes: f54e18f ("isofs: Fix infinite looping over CE entries")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
Link: https://patch.msgid.link/20260419212155.2169382-2-michael.bommarito@gmail.com
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/isofs/rock.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=8356fb821016797f5677cbeee5ddc0d32a95b4be

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

The original Linux kernel CVE announcement for CVE-2026-46303 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46303

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:L/I:N/A:N
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:L
  The Best / paranoid CVSS score: 4.4

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: 3
  Paranoid ActionableScore: 4

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).