* [CVE-2026-89698][MODERATE 7.0] nfsd: widen nfsd_genl_rqstp address fields to sockaddr_storage
@ 2026-09-12 1:46 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-12 1:46 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-89698
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: nfsd: widen nfsd_genl_rqstp address fields to sockaddr_storage
Commit: 03c512f22d3fbe7a3767d6df5e3d88b8e7c105e5
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=03c512f22d3fbe7a3767d6df5e3d88b8e7c105e5
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89698
Analysis date: Fri, 11 Sep 2026 21:46:13 -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-2026-89698 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89698
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-2026-89698 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89698 CHECK WITH IMPACT FROM ORIG NN MODERATE 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-126;*CWE-200;CWE-125;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 out of bounds read in the nfsd rpc_status generic netlink dump can occur because rq_daddr and rq_saddr were stored as 16 byte sockaddr fields but later interpreted as 28 byte IPv6 sockaddr_in6 objects. When an IPv6 NFS client is present, nfsd_genl_rpc_status_compose_msg() may read past the end of the address field and include adjacent structure bytes such as rq_flags or uninitialized tail data in NFSD_A_RPC_STATUS_SADDR6 or NFSD_A_RPC_STATUS_DADDR6 attributes. For the CVSS the PR:L is used because a local unprivileged process in the network namespace can request NFSD_CMD_RPC_STATUS_GET through generic netlink without GENL_ADMIN_PERM. The issue is local rather than directly network reachable, although an IPv6 NFS client connection is part of the affected state. Impact is information disclosure from kernel memory to userspace. There is no direct evidence of integrity impact, availability impact, or privilege escalation from this patch alone.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate (with actual score 5) YES OOB DISK SIMPLEFIX LEAK NETWORK IPV6 KPANIC YES NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
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 positive signals:
* +1 Local unprivileged trigger. The supplied context states that `NFSD_CMD_RPC_STATUS_GET` uses `GENL_CMD_CAP_DUMP` without `GENL_ADMIN_PERM`, so a local unprivileged process in the network namespace can request the dump.
* +1 Concrete user-visible OOB read. `struct sockaddr` is 16 bytes, but the IPv6 path interprets it as `struct sockaddr_in6` and reads `sin6_addr` across bytes 8..24.
* +1 Confidentiality plausible. The out-of-bounds bytes are copied to userspace through `NFSD_A_RPC_STATUS_SADDR6` or `NFSD_A_RPC_STATUS_DADDR6`.
* +1 Practical disclosure chain established. The chain is not merely an internal invalid read: netlink dump request leads to OOB read, then `nla_put_in6_addr()` emits the bytes to userspace.
Paranoid additional signal:
* +1 Potential higher-value kernel data disclosure. The fix also zero-initializes the stack `genl_rqstp` object, which supports concern that uninitialized tail or adjacent stack/structure bytes could otherwise be exposed. This justifies manual review and the higher ActionableScore, but does not establish arbitrary read.
Non-awarded signals:
* RealUAF not awarded. No stale lifetime or use-after-free primitive is shown.
* Integrity not awarded. The patch shows read/disclosure only, no unauthorized write.
* Availability not awarded. No crash, panic, hang, or resource exhaustion is established.
* Arbitrary kernel read not awarded. The read is bounded and layout-dependent.
* Remote reachable bonus not awarded. A remote IPv6 NFS client helps create the affected state, but the actual disclosure is through local generic netlink access.
* Privilege escalation not awarded. No credential, FD theft, write primitive, or authorization bypass is established.
* Namespace-scoped privilege not awarded. This is not a capability-gated namespace operation; the key point is that no admin permission is required for the dump.
3. Reachability analysis
The disclosure path is locally reachable by an unprivileged process in the relevant network namespace because the generic netlink dump command lacks `GENL_ADMIN_PERM`. `HostAdminRequired=NO` is supported by the supplied statement that any unprivileged process in the network namespace can request the status dump.
A prior NFS server setup and an IPv6 NFS client connection are environmental prerequisites for the IPv6 address path to contain relevant data. Those prerequisites affect exposure, but they do not make the netlink disclosure request itself host-admin-only. The issue is not directly exploitable from the network alone, because the attacker needs local netlink access to receive the leaked attributes.
No race or timing condition is required. No special hardware is involved. The vulnerable feature depends on NFSD rpc_status generic netlink support and IPv6 client state.
4. Primitive and severity interpretation
The exact primitive is a bounded out-of-bounds read from a stack/local structure used to compose NFSD RPC status netlink output. The bug is caused by storing IPv6-capable addresses in 16-byte `struct sockaddr` fields and later interpreting them as larger `struct sockaddr_in6` objects.
This is not a UAF, not a refcount bug, and not memory corruption in the write sense. It is a local kernel information disclosure primitive with a concrete userspace readback path. The demonstrated consequence is disclosure of adjacent structure bytes such as `rq_flags`, and the zero-initialization in the fix makes potential uninitialized data exposure plausible enough for manual review.
`PrimitiveClass=CLASS_A` is used as a low-end disclosure-oriented Class A primitive because a concrete unprivileged kernel-to-userspace information disclosure path is established. It is not a Strong Important candidate by itself because the disclosed size and contents appear limited, and no arbitrary read or LPE chain is shown.
`ImportantCandidate=YES` because unprivileged kernel memory disclosure should not be automatically downgraded without reviewing actual leaked bytes and deployment exposure. `AutoDowngradeAllowed=NO` because the issue has a concrete user-visible kernel disclosure primitive, not just an internal bounds bug.
Likely operational severity is Actionable Moderate: not urgent like a demonstrated LPE, but not safe for automatic closure as a harmless low-risk bug.
5. One-sentence report phrase
An unprivileged local process in the network namespace can use the NFSD rpc_status generic netlink dump to receive bytes read past undersized sockaddr fields when IPv6 NFS client state is present, resulting in a bounded kernel information disclosure.
6. Manual review recommendation
MANUAL CHECK REQUIRED
Reason: the bug has a concrete unprivileged disclosure path from kernel memory to userspace, and the zero-initialization change suggests possible uninitialized data exposure that should be reviewed before downgrade.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: nfsd: widen nfsd_genl_rqstp address fields to sockaddr_storage
Commit: 03c512f22d3fbe7a3767d6df5e3d88b8e7c105e5
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=03c512f22d3fbe7a3767d6df5e3d88b8e7c105e5
Commit description:
struct nfsd_genl_rqstp declares rq_daddr and rq_saddr as plain
"struct sockaddr" (16 bytes). When an IPv6 NFS client is connected,
nfsd_genl_rpc_status_compose_msg() casts these fields to
"struct sockaddr_in6 *" (28 bytes) and reads sin6_addr at offset 8..24,
which extends 8 bytes past the end of the 16-byte sockaddr field into
the adjacent rq_flags member. The 16-byte nla_put_in6_addr then ships 8
bytes of truncated IPv6 address followed by 8 bytes of rq_flags to
userspace via the NFSD_A_RPC_STATUS_SADDR6/DADDR6 netlink attributes.
This is reachable by any unprivileged process in the network namespace
because NFSD_CMD_RPC_STATUS_GET uses GENL_CMD_CAP_DUMP without
GENL_ADMIN_PERM.
Fix by widening rq_daddr and rq_saddr to struct sockaddr_storage so the
IPv6 casts operate within bounds, copying sizeof(struct sockaddr_storage)
bytes in the memcpy calls so the full address is captured, and
zero-initializing the genl_rqstp stack variable to prevent leaking
uninitialized tail bytes through netlink.
Fixes: bd9d6a3 ("NFSD: add rpc_status netlink support")
Cc: [email protected]
Assisted-by: Claude:claude-opus-4-6
Signed-off-by: Jeff Layton <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Chuck Lever <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
fs/nfsd/nfsctl.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=03c512f22d3fbe7a3767d6df5e3d88b8e7c105e5
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89698 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89698
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: 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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