* [CVE-2026-97605][LOW] erofs: preserve LZMA decoders on resize failure
@ 2026-09-26 17:57 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-26 17:57 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-97605
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: erofs: preserve LZMA decoders on resize failure
Commit: 604ce546e1b9f35b1f45588004f53fac6b2869c1
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=604ce546e1b9f35b1f45588004f53fac6b2869c1
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97605
Analysis date: Sat, 26 Sep 2026 13:57:37 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-97605 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97605
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: LOW
Manual review required: NO
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-97605 LOW https://www.kernelcve.org/list/?q=CVE-2026-97605 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:N/I:N/A:H';**CWE-476;CWE-703;**CWE-400;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'An EROFS LZMA decoder pool resize can leave a decoder stream with a NULL state when allocation of a replacement decoder fails after other streams were already resized. A later read from an existing LZMA compressed EROFS mount can select that stream and pass NULL to xz_dec_microlzma_reset, causing a kernel crash and local denial of service. The condition requires a partial allocation failure during decoder pool growth and is therefore high complexity. For the CVSS the PR:L paranoid rating assumes a local unprivileged process can access an already mounted vulnerable EROFS image and contribute to memory pressure or trigger filesystem reads after an administrator mounted the image. The issue is not network reachable. Impact is denial of service only. There is no evidence of use after free, out of bounds access, information disclosure, or a privilege escalation primitive.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) YES DISK NOMEMCHK SIMPLEFIX LINUS MEMORY DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 YES NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate**::
The only supported positive signal is a kernel crash or local denial of service. The supplied patch does not establish a stronger corruption, lifetime, ownership, or authorization primitive.
2. Signal breakdown
* +1 Reliable kernel crash or strong DoS. A stream can be returned to the global LZMA decoder pool with `state == NULL`, and a later EROFS decompression path can pass that NULL pointer to `xz_dec_microlzma_reset()`.
* +0 No real UAF. The old decoder is released before allocation in the vulnerable code, but the later failure leaves a NULL state rather than retaining and dereferencing a freed decoder pointer.
* +0 No controlled reclaim, object substitution, arbitrary write, OOB access, callback control, refcount takeover, or structured stale-object use is established.
* +0 No confidentiality or integrity impact is established. The observed primitive is an invalid NULL state and resulting dereference.
* +0 No remote reachability is established. The vulnerable operation is reached through a local EROFS LZMA mount and decoder-pool resize path.
* +0 Local unprivileged trigger is not awarded. A local reader may access an already mounted EROFS filesystem, but the supplied evidence does not establish that the same unprivileged attacker can reliably arrange the vulnerable mount, force the required decoder resize, and induce the required allocation failure.
* +0 No hard-race penalty applies. This is an ordered allocation-failure and state-consistency bug, not a timing race.
* +0 No repeated release or refcount mutation exists. The patch does not show a surviving dangling reference reaching a second `put`, `free`, or refcount operation.
* +0 No extra Availability point is awarded because the same NULL dereference already accounts for the demonstrated crash consequence.
3. Reachability analysis
The vulnerable path requires an EROFS filesystem using LZMA compression and a decoder-pool resize where allocation of a replacement decoder fails after one or more prior streams were successfully resized. The resulting broken stream must then be selected by a later read from an existing EROFS LZMA mount.
Mounting arbitrary filesystem images is commonly privilege-gated, but the supplied patch does not show the complete mount and read privilege boundary. An existing EROFS mount may be readable by below-host-admin users, while creation of the relevant mount may have been performed by an administrator. Therefore HostAdminRequired is UNKNOWN rather than YES or NO.
No namespace-specific capability path is shown. No remote protocol, special hardware, firmware input, sysctl prerequisite, or boot-time configuration prerequisite is established beyond EROFS LZMA support and a vulnerable mounted filesystem. The allocation-failure requirement makes triggering operationally conditional, but this is not a race.
4. Primitive and severity interpretation
The exact primitive is a NULL-pointer dereference caused by invalid decoder-pool state after partial allocation failure. A decoder stream is returned to the global list with `state == NULL`, while the global maximum dictionary size is incorrectly advanced and prevents repair through a retry at the same size.
This is not an active structured-object UAF and not fixed stale storage. The old decoder is not used after free. The failure path leaves an invalid NULL state, which is later consumed by decompression code. There is no concrete second lifetime/refcount mutation, no controlled post-free contents, and no demonstrated memory corruption beyond the invalid dereference.
The appropriate classification is CLASS_C. The demonstrated consequence is local kernel crash or denial of service. Privilege escalation, information disclosure, integrity impact, arbitrary read/write, and controlled corruption remain speculative and are not supported by the patch.
ImportantCandidate is NO because the patch establishes a crash-only invalid-state path without meaningful unresolved exploitation leverage. AutoDowngradeAllowed is YES because no Class A or Class B lifetime/corruption primitive remains for manual exploitation analysis. Operational severity is low-to-ordinary-moderate and depends on use of EROFS LZMA mounts under memory-pressure conditions.
5. One-sentence report phrase
An EROFS LZMA decoder pool resize failure can leave a decoder stream with a NULL state, allowing a later filesystem read to cause a kernel NULL-pointer dereference and local denial of service.
6. Manual review recommendation
NO MANUAL CHECK NEEDED
The patch supports a constrained NULL-pointer dereference and local DoS scenario only. It does not establish a UAF, OOB access, controlled memory corruption, authorization bypass, or privilege-escalation primitive.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: erofs: preserve LZMA decoders on resize failure
Commit: 604ce546e1b9f35b1f45588004f53fac6b2869c1
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=604ce546e1b9f35b1f45588004f53fac6b2869c1
Commit description:
The pool-resize path frees each stream's old decoder before allocating
its replacement. If an allocation fails after some streams have already
been replaced, the failed stream is put back on the list with state ==
NULL. z_erofs_lzma_max_dictsize is still advanced as if the whole
pool had been resized.
An existing LZMA mount can select the broken stream and pass
NULL to xz_dec_microlzma_reset(). A retry at the same size also
skip another resize attempt. Since the global maximum was advanced,
thus, the invalid state is left unrepaired.
Allocate each replacement before freeing the old decoder, temporarily
retaining one old decoder during allocation. Stop at the first failure
and advance z_erofs_lzma_max_dictsize only after all streams satisfy
the request.
Record each stream's dictionary capacity so retries can skip streams
already enlarged before a partial failure.
Fixes: 622cead ("erofs: lzma compression support")
Cc: [email protected]
Signed-off-by: Nikhil Gurudasani <[email protected]>
Reviewed-by: Gao Xiang <[email protected]>
Signed-off-by: Gao Xiang <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
fs/erofs/decompressor_lzma.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=604ce546e1b9f35b1f45588004f53fac6b2869c1
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-97605 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97605
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:H/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 4.7
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: 1
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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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