* [CVE-2026-89657][MODERATE 7.0] libceph: validate OSD extent maps before cursor advance
@ 2026-09-12 10:16 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-12 10:16 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-89657
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: libceph: validate OSD extent maps before cursor advance
Commit: 058ffa81f9440c5b4714685611cf697fd3739ec9
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=058ffa81f9440c5b4714685611cf697fd3739ec9
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89657
Analysis date: Sat, 12 Sep 2026 06:16:30 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate
Manual review required: NO
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89657 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89657
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: NO
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-89657 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89657 CHECK WITH IMPACT FROM ORIG NN IMPORTANT Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:H/UI:N/S:U/C:L/I:L/A:H';*CWE-20;CWE-1284;CWE-617;Other CVSS 'AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6';DESCR 'A malformed authenticated Ceph OSD sparse-read reply can provide an invalid extent map that is not monotonic or does not stay inside the original request range. The client may then advance the message data cursor beyond the request buffer and reach BUG_ON in ceph_msg_data_next from the receive path, causing a kernel crash. For the CVSS the PR:H is used because practical triggering requires a malicious or compromised authenticated Ceph OSD peer rather than only unauthenticated network access to the client. The issue is network reachable within Ceph storage or data center networks where the client accepts replies from OSD peers. Impact is at least denial of service via kernel crash. In the paranoid score, limited confidentiality or integrity impact is kept for manual review sensitivity because the bug involves cursor advancement beyond the request buffer, but the patch does not show an arbitrary write primitive or a clear privilege escalation path.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate (with actual score 5) YES REMOTE DANGER NETWORK KERNEL_PANIC_PLUS_UAF LINUS KPANIC KPANIC LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS YES NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
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:
* +2 Remote reachable authenticated peer input. A malformed Ceph OSD sparse-read reply reaches the kernel Ceph client receive path over the network when the peer is a malicious or compromised authenticated OSD.
* +1 Reliable kernel crash / strong DoS. The described path reaches BUG_ON in ceph_msg_data_next and can crash the kernel client.
* +1 Weak / indirect corruption candidate. The OSD supplied extent map can advance the message-data cursor beyond the original request buffer, creating an invalid active cursor state before the BUG_ON.
Paranoid additional signal:
* +1 Important storage path. The bug is in the Ceph OSD client sparse-read path, where malformed storage-server replies affect kernel-side request buffer cursor handling.
Non-awarded signals:
* RealUAF not awarded. No stale post-lifetime object use is established.
* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Confidentiality and integrity signals not awarded. Cursor advancement beyond the request buffer is concerning, but no disclosure path, directed write, or privilege-escalation primitive is established.
* Extra Availability not awarded. The kernel crash is already counted once.
* Concrete repeated release/refcount not awarded. No first release, surviving exact reference, or second lifetime mutation is present.
* Strong LPE or strong exploitation leverage not awarded. The patch supports malformed input leading to invalid cursor state and BUG_ON, not controlled memory corruption.
* No privilege penalty applied. The attacker role is restricted to an authenticated OSD peer, but this is not host-admin-equivalent privilege on the victim.
3. Reachability analysis
The trigger is a malformed sparse-read reply from a malicious or compromised authenticated Ceph OSD peer. The attacker does not need host administrator privileges on the client, but must be accepted as a trusted OSD peer by the Ceph client. This is not unauthenticated Internet exposure in the usual deployment model.
The issue is network reachable inside Ceph storage or data-center networks where kernel clients communicate with OSDs. Prior Ceph cluster setup and OSD authentication are required, but the vulnerable operation is in the client receive path after that trust relationship exists.
No namespace-scoped local privilege is involved. No special hardware requirement is indicated. No race or narrow timing condition is required.
4. Primitive and severity interpretation
The exact primitive is malformed extent-map validation causing the client to advance a message-data cursor beyond the original sparse-read request buffer. The demonstrated consequence is BUG_ON in ceph_msg_data_next and kernel client crash.
This is not an active structured UAF, not fixed stale storage, and not a concrete repeated release/refcount case. It is best classified as CLASS_C because the established behavior is invalid state and crash/DoS without an independently useful corruption primitive.
The speculative consequence is that cursor movement beyond the request buffer deserves manual review, but the supplied patch does not establish arbitrary read, arbitrary write, controlled reclaim, privilege escalation, or meaningful confidentiality/integrity impact.
ImportantCandidate=NO because the evidence supports actionable remote authenticated DoS, not an Important-preserving corruption or boundary-bypass primitive. AutoDowngradeAllowed=NO because the issue is a network-triggerable kernel crash from a trusted storage peer and should not be automatically closed without checking Ceph exposure and affected deployments.
Likely operational severity: actionable Moderate.
5. One-sentence report phrase
A malformed authenticated Ceph OSD sparse-read reply can provide an invalid extent map that advances the client message-data cursor beyond the request buffer and reaches BUG_ON in ceph_msg_data_next, causing a network-triggerable kernel client DoS from a malicious or compromised OSD peer.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Reason: network-triggerable kernel crash from an authenticated Ceph OSD peer, with invalid cursor advancement beyond the request buffer, but no established UAF, arbitrary write, disclosure, or LPE primitive.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: libceph: validate OSD extent maps before cursor advance
Commit: 058ffa81f9440c5b4714685611cf697fd3739ec9
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=058ffa81f9440c5b4714685611cf697fd3739ec9
Commit description:
net/ceph/osd_client.c:osd_sparse_read() validates that the sparse-read
data length matches the summed extent lengths, but it does not validate
that each OSD-supplied extent is monotonic and lies inside the original
request range. A malformed authenticated OSD reply can advertise a
far-forward nonzero extent offset with a matching data length and make
the client advance the message-data cursor beyond the request buffer.
This reaches the BUG_ON(!*length) assertion in ceph_msg_data_next() from
the client receive path.
Impact: A malicious or compromised authenticated Ceph OSD peer can crash
a kernel Ceph client via a malformed sparse-read reply.
Reject sparse extent maps that overflow, move backwards, overlap, or
extend outside the original sparse-read request before advancing the
cursor.
[ idryomov: perform sparse_extent_map_valid() check a bit earlier,
in CEPH_SPARSE_READ_DATA_LEN instead of CEPH_SPARSE_READ_DATA_PRE
state ]
Cc: [email protected]
Fixes: f628d79 ("libceph: add sparse read support to OSD client")
Assisted-by: Codex:gpt-5-5-xhigh
Signed-off-by: Michael Bommarito <[email protected]>
Reviewed-by: Viacheslav Dubeyko <[email protected]>
Signed-off-by: Ilya Dryomov <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
net/ceph/osd_client.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=058ffa81f9440c5b4714685611cf697fd3739ec9
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89657 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89657
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:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS vector: AV:N/AC:L/PR:H/UI:N/S:U/C:L/I:L/A:H
The Best / paranoid CVSS score: 6
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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