* [CVE-2026-90157][MODERATE REGULAR] bpf: Reject negative optlen in cgroup getsockopt hook [ Upstream
@ 2026-09-17 18:36 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-17 18:36 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-90157
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: bpf: Reject negative optlen in cgroup getsockopt hook [ Upstream
Commit: 5b09d984b38b018b123c3a9e02a96bbc6468dbe5
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5b09d984b38b018b123c3a9e02a96bbc6468dbe5
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90157
Analysis date: Thu, 17 Sep 2026 14:36:36 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline / manual review recommended
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90157 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90157
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 REGULAR
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-2026-90157 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-90157 CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-839;CWE-681;*CWE-20;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'A lower bound validation bug in the cgroup getsockopt BPF kernel-buffer hook allows a BPF program to set ctx optlen to a negative value after the kernel getsockopt handler has run. The negative value can be propagated back to the TCP_ZEROCOPY_RECEIVE getsockopt path and converted to size_t when passed to copy_to_sockptr, which can trigger a hardened usercopy bytes greater than INT_MAX warning. For the CVSS the PR:L is used in the paranoid score because delegated BPF access or a constrained service account may be sufficient in some deployments, although the typical base case requires administrative BPF privileges to load and attach the cgroup program. The issue is local and is not directly network reachable because the attacker needs control over the cgroup getsockopt BPF hook and a local getsockopt call path. Impact is primarily denial of service through warning or possible panic_on_warn behavior, with no concrete evidence of a reliable information disclosure or privilege escalation primitive from the provided patch.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3) YES WARNONLY BPF SIMPLEFIX INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 3
* Paranoid score: 3
* Final recommended bucket: **Borderline / manual review recommended**::
No floor or cap changed the score. Validation-only cap is not binding because the score is below the cap.
2. Signal breakdown
Conservative positive signals:
* +1 Weak or indirect corruption candidate. A negative signed optlen can be reinterpreted as a large size_t and reach copy_to_sockptr through the TCP_ZEROCOPY_RECEIVE getsockopt path.
* +1 Memory/copy-size invariant restoration. The patch restores the missing lower-bound validation between ctx.optlen, the original optlen, and the eventual copy size.
Paranoid additional signal:
* +1 Potential availability impact in panic_on_warn or hardened-usercopy-fatal configurations. The established symptom is a hardened usercopy bytes greater than INT_MAX warning, and some deployments treat such warnings as fatal.
Non-awarded material signals:
* No RealUAF. The patch does not establish a stale object, post-lifetime access, double release, or refcount lifetime mutation.
* No controlled reclaim, arbitrary write, OOB write, or directed kernel corruption is demonstrated.
* No confidentiality or integrity signal is awarded because the hardened usercopy path blocks the oversized copy rather than establishing a data disclosure or write primitive.
* No local unprivileged trigger is awarded because the complete cgroup BPF load and attach path is privilege-gated and below-host-admin reachability is not established.
* No remote reachability is awarded. This requires local control over the cgroup getsockopt BPF hook and a local getsockopt path.
* No extra availability point is awarded beyond the paranoid warning-to-fatal interpretation.
* BPF privilege-gated control-plane cap was considered. It does not raise the score and only prevents unsupported escalation.
3. Reachability analysis
The vulnerable path requires a cgroup getsockopt BPF program that can modify ctx.optlen after the kernel getsockopt handler has completed. The practical trigger also involves the TCP_ZEROCOPY_RECEIVE getsockopt kernel-buffer path.
Loading and attaching cgroup BPF programs is normally privilege-gated by BPF and cgroup attachment permissions such as CAP_BPF, CAP_NET_ADMIN, or CAP_SYS_ADMIN depending on kernel and product policy. The supplied input does not prove that an ordinary unprivileged user can complete the full load, attach, and trigger sequence.
HostAdminRequired is UNKNOWN rather than YES because the exact evaluated product policy and capability scope are not fully supplied. HostAdminRequired is not NO because below-host-admin reachability is not positively established.
NamespaceScopedPrivilege is UNKNOWN. The input does not establish that all required BPF loading, cgroup attachment, and getsockopt triggering operations are available inside attacker-created namespaces.
No special hardware is required. No race or narrow timing window is involved. Prior privileged setup may exist if an administrator has already attached a vulnerable cgroup BPF program, but attacker-controlled exploitation requires the attacker to influence that program or its attachment.
4. Primitive and severity interpretation
The exact primitive is missing lower-bound validation of ctx.optlen in the cgroup getsockopt kernel-buffer hook. A BPF program can set optlen negative, and that value can later be converted to size_t in a copy path.
This is not a UAF and not active structured stale-object corruption. It is best classified as CLASS_C because the demonstrated behavior is invalid-state handling leading to a hardened usercopy warning, with possible DoS only under fatal-warning configurations.
The demonstrated consequence is warning/DoS. The speculative consequence would be stronger memory exposure from a huge copy size, but the supplied patch context indicates hardened usercopy catches the oversized length, so that stronger primitive is not established.
ImportantCandidate is NO because there is no concrete kernel memory corruption, authorization bypass, ownership violation, UAF, repeated release, or proven LPE primitive. AutoDowngradeAllowed is YES because the established issue is validation-only and crash/warning-oriented, without unresolved meaningful exploitation leverage.
Likely operational severity is ordinary low-to-moderate, but manual review is still recommended because the bug sits in a BPF-mediated kernel copy-size path and the paranoid score reaches the actionable-review boundary for some policies.
5. One-sentence report phrase
A cgroup getsockopt BPF program can set ctx.optlen to a negative value in the TCP_ZEROCOPY_RECEIVE kernel-buffer path, causing signed-to-unsigned size reinterpretation in copy_to_sockptr and a hardened usercopy warning or possible local DoS.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Reason: the issue is not an Important candidate from the supplied evidence, but it involves BPF-controlled length validation feeding a kernel copy helper, so a focused review of copy_to_sockptr failure behavior and product-specific BPF privilege policy is appropriate.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: bpf: Reject negative optlen in cgroup getsockopt hook [ Upstream
Commit: 5b09d984b38b018b123c3a9e02a96bbc6468dbe5
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5b09d984b38b018b123c3a9e02a96bbc6468dbe5
Changed files:
kernel/bpf/cgroup.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=5b09d984b38b018b123c3a9e02a96bbc6468dbe5
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90157 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90157
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:H/UI:N/S:U/C:N/I:N/A:L
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 5.5
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: 2
Paranoid ActionableScore: 3
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: NO
Published priority for this report (same as in Subject): MODERATE REGULAR
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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