* [CVE-2026-98531][MODERATE 7.0] ipv6: sr: enforce exact attribute length for SEG6_ATTR_DST
@ 2026-10-24 12:58 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-24 12:58 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98531
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ipv6: sr: enforce exact attribute length for SEG6_ATTR_DST
Commit: 050a0aa3c80907b8c60a396b7e04d48d8b1a9e70
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=050a0aa3c80907b8c60a396b7e04d48d8b1a9e70
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98531
Analysis date: Sat, 24 Oct 2026 08:58:19 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
A CAP_NET_ADMIN-capable local actor can use an undersized SEG6 attribute to disclose 16 bytes of uninitialized kernel heap memory through the corresponding GET command.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98531 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98531
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-2026-98531 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98531 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=MODERATE_KPANIC RESULT=SAME V39_AEGIS_ONE_STEP_UP=MODERATE->MODERATE_KPANIC (final reconciliation agrees; DECISION: both MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N';CWE-125;*CWE-200;CWE-1284;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '5.5';DESCR 'An undersized SEG6_ATTR_DST can make seg6_genl_set_tunsrc copy 16 bytes from a shorter Generic Netlink attribute, causing an out of bounds read beyond the attribute payload into uninitialized skb head memory. The copied bytes are stored as tun_src and returned through SEG6_CMD_GET_TUNSRC, providing a demonstrated kernel memory disclosure primitive. For the CVSS the PR:L value reflects that this is a local Generic Netlink control operation normally requiring CAP_NET_ADMIN, including a delegated capability in a user or network namespace. The issue is not directly reachable through ordinary IPv6 packet traffic. Base impact is limited confidentiality disclosure with no supported write or availability primitive. The paranoid score uses C:H because repeated requests may expose additional sensitive kernel data, although the content of each 16 byte sample is not controlled or guaranteed. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 5.5 and the production ActionableScore returned 2 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were ActionableScore thresholds stage MODERATE_KPANIC to MODERATE because the ActionableScore threshold rule was applied. final reconciliation stage MODERATE to MODERATE_KPANIC because the cross model evidence reconciliation rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 and V39_AEGIS_ONE_STEP_UP and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 3.3 and ActionableScore 2 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) MAYBE REMOTE OOB LEAK NETWORK IPV6 DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 KPANIC V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=2
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=YES
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=CONFIRMED
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 2.
* Conservative score: 2; no floor or cap applied.
* Raw paranoid score: 2.
* Paranoid score: 2; repeated sampling does not establish broader or high-value disclosure.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* +1 — Concrete limited OOB-read/disclosure primitive: `kmemdup()` reads 16 bytes despite a potentially zero-length attribute.
* +1 — Confidentiality impact: the demonstrated GET operation returns the copied uninitialized kernel heap bytes to userspace.
* +1 — Practical chain: short SET attribute → OOB read → storage in `tun_src` → GET disclosure.
* -1 — Reduced/delegated privilege: supplied evidence identifies CAP_NET_ADMIN, including namespace/delegated capability, rather than ordinary unprivileged access.
* No write, UAF, crash, authorization bypass, attacker-selected address, or integrity impact is shown.
* No extra confidentiality point: repeated requests may sample additional bytes, but sensitive contents or a major disclosure are not established.
* B5-R and B3-PENDING do not apply: this is a read, not a retry-accumulated or shared-backing write.
3. Reachability analysis
The vulnerable operation is a local Generic Netlink SEG6 control-plane request, not ordinary IPv6 packet input. Supplied evidence places SET/GET behind CAP_NET_ADMIN and indicates that delegated namespace capability can suffice; thus host-admin-equivalent power and host UID 0 are not inherently required. The complete path is namespace-scoped according to the supplied summary, although the capability checks and operation table are not visible in the patch itself. No hardware, race, retry, or prior host-created object is required.
4. Primitive and severity reading
The exact primitive is a bounded 16-byte heap OOB read followed by an explicit userspace readback. This is CLASS_B because it is a real information-disclosure primitive, but it is constrained in size and source, with no attacker-selected kernel address or demonstrated sensitive victim. The shown effect is kernel heap disclosure; high-value secrets, arbitrary reads, writes, LPE, and availability effects remain unproven. ImportantCandidate is NO and auto-downgrade is allowed because the impact is bounded and understood rather than an unresolved strong corruption primitive.
5. One-sentence report phrase
A CAP_NET_ADMIN-capable local actor can use an undersized SEG6 attribute to disclose 16 bytes of uninitialized kernel heap memory through the corresponding GET command.
6. Manual review advice
MANUAL CHECK RECOMMENDED
Confirm the exact namespace capability checks and whether repeated allocation shaping materially broadens the disclosed data.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: ipv6: sr: enforce exact attribute length for SEG6_ATTR_DST
Commit: 050a0aa3c80907b8c60a396b7e04d48d8b1a9e70
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=050a0aa3c80907b8c60a396b7e04d48d8b1a9e70
Commit description:
In seg6_genl_policy, SEG6_ATTR_DST is defined with .type = NLA_BINARY and
.len = sizeof(struct in6_addr). For NLA_BINARY, .len only enforces the
maximum payload length and permits shorter payloads (e.g., 0 bytes).
When seg6_genl_set_tunsrc() copies sizeof(struct in6_addr) bytes via
kmemdup(val, sizeof(*val), GFP_KERNEL), a short SEG6_ATTR_DST attribute
triggers a 16-byte out-of-bounds read past skb->tail into uninitialized
skb->head memory, which is stored in sdata->tun_src and leaked back to
userspace via SEG6_CMD_GET_TUNSRC.
Switch SEG6_ATTR_DST in seg6_genl_policy to
NLA_POLICY_EXACT_LEN(sizeof(struct in6_addr)) so that generic netlink
validation rejects any attribute whose length is not exactly
sizeof(struct in6_addr) with -ERANGE.
Tested in QEMU against Linux 7.3.0-rc3 by sending a SEG6_CMD_SET_TUNSRC
Generic Netlink message with a 0-byte SEG6_ATTR_DST attribute followed
by SEG6_CMD_GET_TUNSRC. On the unfixed kernel, SEG6_CMD_SET_TUNSRC
succeeds (err = 0) and SEG6_CMD_GET_TUNSRC leaks 16 bytes of
uninitialized kernel heap memory (tun_src =
836a61ecc4d25a1042a8d60411cfb378); with this patch applied,
SEG6_CMD_SET_TUNSRC is rejected by netlink policy validation with
-ERANGE (-34) and tun_src remains zeroed.
Fixes: 915d7e5 ("ipv6: sr: add code base for control plane support of SR-IPv6")
Cc: [email protected]
Signed-off-by: Hui Peng <[email protected]>
Reviewed-by: Hangbin Liu <[email protected]>
Reviewed-by: Justin Iurman <[email protected]>
Reviewed-by: Andrea Mayer <[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/ipv6/seg6.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=050a0aa3c80907b8c60a396b7e04d48d8b1a9e70
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98531 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98531
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:L/UI:N/S:U/C:L/I:N/A:N
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
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: unknown
Paranoid ActionableScore: 2
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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