[CVE-2026-64317][MODERATE 7.0] isofs: bound Rock Ridge symlink components to the SL record

[CVE-2026-64317][MODERATE 7.0] isofs: bound Rock Ridge symlink components to the SL record

[AL-KERNEL]

CVE: CVE-2026-64317
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: isofs: bound Rock Ridge symlink components to the SL record
Commit: 1015e1c4b2fadd9c09704e24738e46598778c869
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1015e1c4b2fadd9c09704e24738e46598778c869
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64317
Analysis date: Sat, 25 Jul 2026 13:18:55 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A crafted ISO 9660 Rock Ridge symlink can cause an out-of-bounds kernel read whose bytes may be exposed through readlink(), making this a practical local or automount-assisted kernel memory disclosure issue.

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

The original Linux kernel CVE announcement for CVE-2026-64317 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64317

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

CVE-2026-64317	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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:N/A:L';CWE-125;CWE-126;*CWE-200;*CWE-20;Other CVSS 'AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:L';BEST CVSS score: '6.1';DESCR 'A malformed Rock Ridge SL symlink record in an ISO 9660 filesystem can make the isofs parser read past the end of the SL record. get_symlink_chunk() can then copy out-of-bounds bytes into the symlink target returned by readlink(), which may disclose adjacent kernel memory to user space. For the CVSS the PR:N is used for the paranoid interpretation because attacker controlled ISO media or an ISO image may be supplied without an authenticated local account when desktop automount or user assisted mounting is available. The issue is not directly network reachable and requires the crafted filesystem image to be mounted or automounted. Impact is primarily confidentiality loss from kernel memory disclosure, with possible limited availability impact if the malformed record triggers a fault.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	WRITE OOB DISK IMPROVEONLY LINUS KPANIC  KPANIC LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS 	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

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

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. A local user may be able to trigger parsing by supplying or accessing a crafted ISO image, especially on desktop systems with user-assisted or udisks2 automount behavior.
* Confidentiality impact plausible: +1. The patch description gives a concrete OOB read where bytes can be copied into the symlink body returned by readlink().
* Important filesystem/storage path: +1. The bug is in kernel filesystem metadata parsing for ISO 9660 Rock Ridge symlinks.
* Broad/common exposure: +1. ISO images and removable media are common enough that this should not be treated as a rare-only subsystem.

Paranoid additional signal:

* Crafted filesystem metadata reachable through untrusted media: +1. The attacker controls the on-disk SL record and may reach kernel parsing through automount or user-assisted mounting, making this more actionable than a purely privileged mount-only bug.

Non-applied signals:

* Remote reachable: +0. This is not directly network-triggerable.
* Strong memory corruption: +0. The primitive is an OOB read and disclosure, not OOB write, UAF, double-free, or controlled overwrite.
* Privilege escalation plausible: +0. No write primitive, reclaim primitive, refcount abuse, callback control, or type confusion is shown.
* Reliable kernel crash / strong DoS: +0. Availability impact is possible but not the main demonstrated primitive.

## 3. Reachability analysis

The bug is triggered by parsing a crafted ISO 9660 Rock Ridge SL symlink record and then calling readlink() on the affected symlink. In strict server deployments, mounting such an image may require CAP_SYS_ADMIN, which would reduce practical reachability. However, the commit explicitly notes common desktop automount behavior where untrusted removable media may be mounted without the user holding CAP_SYS_ADMIN directly. Containers and namespaces do not generally make this safer unless filesystem mounting and automount helpers are restricted. Realistic exploitation requires getting the crafted filesystem image mounted or automounted and then causing the malformed symlink to be resolved or read.

## 4. Severity interpretation

This behaves like an actionable Moderate issue rather than an ordinary Low or generic DoS. The important point is that the patch describes a concrete kernel memory disclosure path: an OOB read of up to 255 bytes can be copied into a symlink target returned to user space. It does not currently justify Important-class LPE scoring because there is no demonstrated write primitive or object lifetime corruption. The paranoid score is elevated because untrusted filesystem images are a historically important kernel attack surface and automount can reduce the effective privilege requirement.

## 5. One-sentence report phrase

A crafted ISO 9660 Rock Ridge symlink can cause an out-of-bounds kernel read whose bytes may be exposed through readlink(), making this a practical local or automount-assisted kernel memory disclosure issue.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Manual review is required because this is a concrete OOB read with a user-visible kernel memory disclosure path, and practical exposure depends on product-specific automount, desktop, removable-media, and user-mount policies.

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

Patch: isofs: bound Rock Ridge symlink components to the SL record
Commit: 1015e1c4b2fadd9c09704e24738e46598778c869
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1015e1c4b2fadd9c09704e24738e46598778c869

Commit description:

get_symlink_chunk() and the SL handling in
parse_rock_ridge_inode_internal() walk the variable-length components of
a Rock Ridge "SL" (symbolic link) record.  Each component is a two-byte
header (flags, len) followed by len bytes of text, so it occupies
slp->len + 2 bytes.  Both loops read slp->len and advance to the next
component, and get_symlink_chunk() additionally does
memcpy(rpnt, slp->text, slp->len), but neither checks that the component
lies within the SL record before dereferencing it.

A crafted SL record whose component declares a len that runs past the
record (rr->len) therefore triggers an out-of-bounds read of up to 255
bytes.  When the record sits at the tail of its backing buffer - for
example a small kmalloc()ed continuation block reached through a CE
record - the read crosses the allocation; get_symlink_chunk() then
copies the out-of-bounds bytes into the symlink body returned to user
space by readlink(), disclosing adjacent kernel memory.

ISO 9660 images are routinely mounted from untrusted removable media -
desktop environments auto-mount them (e.g. via udisks2) without
CAP_SYS_ADMIN - so the record contents are attacker-controlled.

Reject any component that does not fit in the remaining record bytes
before using it.  In get_symlink_chunk() return NULL, like the existing
output-buffer (plimit) checks, so a malformed record makes readlink()
fail with -EIO rather than silently returning a truncated target; in
parse_rock_ridge_inode_internal() stop the inode-size walk.

Fixes: 1da177e ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Suggested-by: Michael Bommarito <michael.bommarito@gmail.com>
Signed-off-by: Bryam Vargas <hexlabsecurity@proton.me>
Link: https://patch.msgid.link/20260607011823.217748-1-hexlabsecurity@proton.me
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=1015e1c4b2fadd9c09704e24738e46598778c869

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

The original Linux kernel CVE announcement for CVE-2026-64317 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64317

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:N/UI:R/S:U/C:H/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:L
  The Best / paranoid CVSS score: 6.1

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).