* [CVE-2026-99064][IMPORTANT] cipso: adjust cached option offsets when removing CIPSO
@ 2026-10-27 5:46 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-27 5:46 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-99064
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: NO
Patch: cipso: adjust cached option offsets when removing CIPSO
Commit: b965977126a90e01825814c859ba4788691eddd3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b965977126a90e01825814c859ba4788691eddd3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99064
Analysis date: Tue, 27 Oct 2026 01:46:48 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
CIPSO deletion leaves stale IPv4 option offsets that can make later kernel option processing use packet data as a copy length and write beyond fixed option storage.
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ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99064 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99064
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: IMPORTANT
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-2026-99064 IMPORTANT https://www.kernelcve.org/list/?q=CVE-2026-99064 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT IMPORTANT AEGIS_AS=4 LEGACY=IMPORTANT RESULT=SAME (final reconciliation agrees; DECISION: both IMPORTANT) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-125;*CWE-20;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '8.1';DESCR 'Removing a CIPSO option leaves cached offsets for later IPv4 options unchanged even though their bytes have moved toward the start of the header. Consumers such as ip_forward_options and __ip_options_echo can consequently access packet bytes at a stale location. In __ip_options_echo an attacker influenced byte may be interpreted as an option length and copied into fixed size option storage, creating a plausible out of bounds write with kernel crash and possible confidentiality or integrity consequences. For the CVSS the PR:N value is selected because a sender does not need an authenticated local account when crafted IPv4 packets can reach a host configured to process and remove CIPSO labels. AC:H reflects the required CIPSO or NetLabel configuration, valid option layout, and a downstream path that consumes the stale metadata. Automated impact decision path. The original SimpleNet classifier selected IMPORTANT. The primary LLM estimated paranoid CVSS 8.1 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were KP and FD specialist checks stage IMPORTANT to IMPORTANT because a specific evidence based protection or manual review veto was applied. final reconciliation stage IMPORTANT to IMPORTANT because KP specialist did not establish a qualifying panic. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. Exact triggered rule markers were V33_ACTIVE_STATE_BOUNDARY_CANDIDATE and IMPORTANT_CANDIDATE_MANUAL_REVIEW and KP_ONLY_DOWNGRADE_VETO and V42_LEGACY_CLASSA_FD_VETO and MANUAL_REVIEW_REQUIRED and KPANIC_UNSUPPORTED_REMOVED. The independent weaker Aegis shadow evaluated CVSS 4.7 and ActionableScore 4 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was IMPORTANT. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is IMPORTANT.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) MAYBE REMOTE SIMPLEFIX NETWORK LINUS PACKET V33_ACTIVE_STATE_BOUNDARY_CANDIDATE IMPORTANT_CANDIDATE_MANUAL_REVIEW KP_ONLY_DOWNGRADE_VETO V42_LEGACY_CLASSA_FD_VETO MANUAL_REVIEW_REQUIRED KPANIC_UNSUPPORTED_REMOVED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 4.
* Conservative score: 5; manual-review safety floor applied because an attacker-influenced heap/structured-storage OOB write is supported.
* Raw paranoid score: 4.
* Paranoid score: 5; no additional speculative remote, disclosure, or LPE points.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
* +2 strong corruption primitive: CIPSO removal moves following IPv4 options but leaves `srr`, `rr`, `ts`, and `router_alert` offsets stale. `__ip_options_echo()` can read an attacker-influenced byte as an option length and copy that amount into fixed-size option storage, supporting an OOB write.
* +1 reliable kernel crash/strong DoS plausible from the resulting oversized kernel copy.
* +1 packet-processing path: the corrupted metadata is consumed by forwarding/option-echo processing, including `ip_forward_options()` and `__ip_options_echo()`.
* No remote-reachability bonus: the supplied material does not establish how an attacker causes the host to remove CIPSO labels or whether required NetLabel policy is already configured.
* No C/I, arbitrary-write, disclosure, controlled-target, or LPE bonus. The write is attacker-influenced but its adjacent victim and security effect are unproven.
* NEW52 B5-R does not apply: no retry-accumulated index is involved. B3-PENDING and B4-PENDING also do not apply.
3. Reachability analysis
The packet contents and misplaced length byte can be attacker-influenced, but the complete trigger requires a path that accepts and removes CIPSO before a later option consumer runs. The patch does not resolve whether that setup requires host administration, whether it can be delegated through a namespace, or whether an unauthenticated network sender can exercise the full chain. No special hardware or race is involved.
4. Primitive and severity reading
The primitive is corrupted active IPv4 option metadata followed by a bounded-source but potentially oversized copy into fixed-size kernel option storage. This is not a UAF and not merely passive metadata corruption: later privileged kernel packet processing consumes the stale offset. The OOB write supports CLASS_A, while exact overwrite extent, adjacent victim, and non-crash exploitation remain unresolved. The credible but unknown packet-to-host trust boundary requires mandatory review and prevents automatic downgrade.
5. One-sentence report phrase
CIPSO deletion leaves stale IPv4 option offsets that can make later kernel option processing use packet data as a copy length and write beyond fixed option storage.
6. Manual review advice
MANUAL CHECK REQUIRED
Confirm the CIPSO-removal call path, attacker-controlled packet reachability, destination object layout, maximum copy length, and whether forwarding or echo processing crosses a namespace or external-to-host trust boundary.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: cipso: adjust cached option offsets when removing CIPSO
Commit: b965977126a90e01825814c859ba4788691eddd3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b965977126a90e01825814c859ba4788691eddd3
Commit description:
cipso_v4_skbuff_delattr() removes the CIPSO bytes but does not adjust
cached offsets for options that follow them.
For example, with a valid 10-byte CIPSO option followed by a seven-byte
RR option, parsing records rr at offset 30. Removing CIPSO moves RR to
offset 20, while the cached offset remains 30. Consumers such as
ip_forward_options() and __ip_options_echo() then access the wrong bytes;
the latter may interpret packet data as the option length and copy it into
fixed-size option storage.
Mirror cipso_v4_delopt() and subtract cipso_len from the srr, rr, ts and
router_alert offsets when they follow CIPSO. cipso_len is the distance
the first memmove() shifts those options. The later header move and
network-header reset relocate the bytes and their offset base together.
Fixes: 89aa361 ("cipso: make cipso_v4_skbuff_delattr() fully remove the CIPSO options")
Cc: [email protected]
Reviewed-by: Ondrej Mosnáček <[email protected]>
Signed-off-by: Daehyeon Ko <[email protected]>
Acked-by: Paul Moore <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
net/ipv4/cipso_ipv4.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=b965977126a90e01825814c859ba4788691eddd3
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99064 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99064
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:H/PR:N/UI:N/S:U/C:L/I:L/A:H
The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
The Best / paranoid CVSS score: 8.1
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: unknown
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: IMPORTANT
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): IMPORTANT
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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