* [CVE-2023-53526][MODERATE 7.0] jbd2: check 'jh->b_transaction' before removing it from checkpoint
@ 2026-09-09 6:32 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-09 6:32 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2023-53526
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: jbd2: check 'jh->b_transaction' before removing it from checkpoint
Commit: ef5fea70e5915afd64182d155e72bfb4f275e1fc
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ef5fea70e5915afd64182d155e72bfb4f275e1fc
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2023-53526
Analysis date: Wed, 09 Sep 2026 02:32:13 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2023-53526 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2023-53526
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.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2023-53526 MODERATE https://www.kernelcve.org/list/?q=CVE-2023-53526 CHECK WITH IMPACT FROM ORIG NN LOW 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:H/A:H';CWE-362;CWE-367;CWE-703;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:L';BEST CVSS score: '6.3';DESCR 'A race in jbd2 checkpoint handling can remove a journal head from an old checkpoint list even after it has been attached to a new active transaction. If a crash or power loss happens before the new transaction is committed, the journal head can be lost on the next mount and the ext4 filesystem image may become corrupted. For the CVSS the PR:L is used because a local user with write access to the filesystem may be able to contribute to the required filesystem activity, although reliable triggering depends on timing, checkpoint pressure, and crash or power loss conditions. The issue is not network reachable and does not indicate kernel memory corruption or privilege escalation. Impact is mainly integrity loss through filesystem corruption and possible availability impact if the filesystem becomes inconsistent or unusable.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate (with actual score 5) MAYBE DISK RACE CVEOUTDATED KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
1. ActionableScore
* Raw conservative score: 4
* Conservative score: 4. No floor or cap applied.
* Raw paranoid score: 5
* Paranoid score: 5. No floor or cap applied.
* Final recommended bucket: **Actionable Moderate**::
2. Signal breakdown
Conservative signals:
* +1 Local below-host-admin reachability. A local user with write access to an ext4 filesystem can generate filesystem write activity that reaches jbd2 transaction and checkpoint logic.
* +1 Active journal state consistency violation. The journal head can be removed from an old checkpoint list even though it has already been attached to a new active transaction.
* +1 Filesystem/storage metadata corruption. The supplied sequence directly describes ext4 image corruption after journal state is lost.
* +1 Important filesystem/storage path. jbd2 checkpointing and ext4 journal recovery are core integrity paths.
* +1 Integrity plausible. The demonstrated consequence is persistent filesystem image corruption or data loss after power loss.
* -1 Hard timing and external failure condition. The harmful outcome depends on a specific interleaving plus crash or power cut before the second transaction is committed.
Paranoid additional signal:
* +1 Availability plausible. If the ext4 image is corrupted, later mount or recovery can fail or require administrative repair, creating persistent availability impact distinct from ordinary transient failure.
Important non-awarded signals:
* RealUAF not awarded. The patch establishes journal state loss and checkpoint list inconsistency, not kernel heap use-after-free.
* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Privilege escalation not demonstrated.
* Remote reachability not established.
* Confidentiality impact not awarded.
* Strong LPE or Class A corruption not awarded.
* Race penalty is applied because the supplied sequence depends on a specific timing window and crash or power loss condition, not merely because the bug is called a race.
* Extra availability is only used in the paranoid score because persistent unusability is plausible but not guaranteed by every trigger.
Repeated release/refcount checklist:
* First release can end lifetime: not applicable.
* Exact same reference survives: not applicable.
* Second lifetime/refcount mutation: not applicable.
* Concrete repeated release/refcount +1 awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 applied: no.
3. Reachability analysis
The evaluated attacker is a local user with write access to the affected ext4 filesystem. Such a user can create filesystem activity that participates in jbd2 transactions. The complete demonstrated corruption sequence also depends on checkpoint pressure or reclaim behavior and on a crash or power loss before the newer transaction is committed.
Host administrator privilege is not positively required for the filesystem write portion of the path, so HostAdminRequired=NO. However, reliable reproduction may be easier with privileged operations such as forced drop_caches or controlled crash/power interruption. This affects reliability and timing, not the basic below-host-admin filesystem reachability.
No network trigger is established. Namespace-scoped privilege is not relevant to the supplied path. No special hardware is required. The race is not a simple single syscall crash and depends on a specific ordering between commit, write access, checkpoint removal, and crash or power loss.
4. Primitive and severity interpretation
The exact primitive is an active filesystem journal consistency violation. A journal_head can be removed from a checkpoint list while it is already associated with a new active transaction. This can make the old transaction appear checkpointed and complete while the newer transaction has not yet committed, causing the journal head to be lost after a later crash or power loss.
This is not an ordinary stale cleanup dereference and not a kernel memory UAF. It is also not a repeated release/refcount bug. It is best treated as CLASS_B because it corrupts active filesystem journal state and can lead to persistent ext4 image corruption, but the supplied evidence does not establish controlled kernel memory corruption, arbitrary write, privilege escalation, or a cross-file ownership/COW bypass.
Demonstrated consequence: ext4 filesystem image corruption or data loss after an unlucky ordering and power loss/crash.
Speculative consequence: broader availability impact if the corrupted filesystem later requires repair or cannot be mounted cleanly.
ImportantCandidate=NO because there is no memory corruption, authorization bypass, LPE, shared-page ownership violation, or demonstrated protected-resource compromise. ManualReview=REQUIRED because persistent filesystem integrity corruption in ext4/jbd2 is operationally significant and should not be automatically dismissed as a trivial DoS. AutoDowngradeAllowed=NO because an actionable filesystem integrity issue would be lost by automatic closure.
5. One-sentence report phrase
A race in jbd2 checkpoint handling can remove a journal head from the checkpoint list while it belongs to a new active transaction, causing ext4 image corruption or data loss after a crash or power loss before the new transaction is committed.
6. Manual review recommendation
MANUAL CHECK REQUIRED
Reason: the issue affects ext4/jbd2 journal integrity and can cause persistent filesystem corruption, even though no kernel memory corruption or privilege escalation primitive is established.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: jbd2: check 'jh->b_transaction' before removing it from checkpoint
Commit: ef5fea70e5915afd64182d155e72bfb4f275e1fc
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ef5fea70e5915afd64182d155e72bfb4f275e1fc
Commit description:
Following process will corrupt ext4 image:
Step 1:
jbd2_journal_commit_transaction
__jbd2_journal_insert_checkpoint(jh, commit_transaction)
// Put jh into trans1->t_checkpoint_list
journal->j_checkpoint_transactions = commit_transaction
// Put trans1 into journal->j_checkpoint_transactions
Step 2:
do_get_write_access
test_clear_buffer_dirty(bh) // clear buffer dirty，set jbd dirty
__jbd2_journal_file_buffer(jh, transaction) // jh belongs to trans2
Step 3:
drop_cache
journal_shrink_one_cp_list
jbd2_journal_try_remove_checkpoint
if (!trylock_buffer(bh)) // lock bh, true
if (buffer_dirty(bh)) // buffer is not dirty
__jbd2_journal_remove_checkpoint(jh)
// remove jh from trans1->t_checkpoint_list
Step 4:
jbd2_log_do_checkpoint
trans1 = journal->j_checkpoint_transactions
// jh is not in trans1->t_checkpoint_list
jbd2_cleanup_journal_tail(journal) // trans1 is done
Step 5: Power cut, trans2 is not committed, jh is lost in next mounting.
Fix it by checking 'jh->b_transaction' before remove it from checkpoint.
Cc: [email protected]
Fixes: 46f881b ("jbd2: fix a race when checking checkpoint buffer busy")
Signed-off-by: Zhihao Cheng <[email protected]>
Signed-off-by: Zhang Yi <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Theodore Ts'o <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
fs/jbd2/checkpoint.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=ef5fea70e5915afd64182d155e72bfb4f275e1fc
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2023-53526 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2023-53526
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:H/A:L
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H
The Best / paranoid CVSS score: 6.3
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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