* [CVE-2026-89477][MODERATE 7.0] sctp: fix NULL deref on untransmitted RECONF completion
@ 2026-09-12 2:39 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-12 2:39 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-89477
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: sctp: fix NULL deref on untransmitted RECONF completion
Commit: 77ea60f2d24002c308f224db44a4542c466489af
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=77ea60f2d24002c308f224db44a4542c466489af
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89477
Analysis date: Fri, 11 Sep 2026 22:39:45 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
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-2026-89477 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89477
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-2026-89477 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89477 CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';**CWE-476;*CWE-20;CWE-754;BEST CVSS score: '7.5';DESCR 'A NULL pointer dereference in SCTP stream reconfiguration can occur when completion handling matches a pending RECONF chunk that has been published in asoc strreset_chunk but has not yet been transmitted, leaving chunk transport as NULL. A remote SCTP peer can trigger this by sending RECONF content in an ordering where a response is processed before the pending outbound RECONF chunk has a transport assigned, for example by combining relevant RECONF parameters or chunks in one packet. This reaches timer_delete on a NULL transport pointer in softirq context and can crash the kernel (DoS). For the CVSS the PR:N is selected because the remote peer does not need local user access or privileges on the target beyond network reachability to an SCTP association. The issue is network reachable when SCTP is enabled and exposed, although SCTP services are often limited to telecom, clustering, or controlled internal networks rather than the public Internet. Impact is denial of service via kernel crash, with no demonstrated confidentiality or integrity impact from the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4) YES KASAN OOB NULLPTR NETWORK KPANIC PACKET KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=4
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=REQUIRED
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 4
* Conservative score: 4. No floor or cap applied.
* Raw paranoid score: 4
* Paranoid score: 4. No floor or cap applied.
* Final recommended bucket: **Borderline / manual review recommended**::
2. Signal breakdown
Positive signals:
* +2 Remote reachable / directly network-triggerable. The commit explicitly states that a peer needs neither ASCONF nor local help and can trigger the NULL dereference with crafted RECONF ordering or multiple RECONF chunks in one packet.
* +1 Reliable kernel crash / strong DoS. The supplied trace shows NULL pointer dereference in timer_delete from softirq context, with a kernel panic/crash outcome.
* +1 Networking packet-processing path. The vulnerable path is reached from SCTP packet receive and RECONF processing, not only from a local control-plane ioctl.
Non-awarded signals:
* Real UAF not awarded. The primitive is a NULL transport pointer dereference, not a stale post-lifetime object use.
* Controlled reclaim not demonstrated.
* Arbitrary or directed kernel write not demonstrated.
* Confidentiality and integrity impact not awarded. The evidence supports C:N/I:N and A:H style impact only.
* Strong LPE or weak LPE concern not awarded. There is no concrete post-crash exploitation primitive.
* Extra availability point not awarded because the same kernel crash is already counted once.
* Race or timing penalty not applied. The remote trigger is an ordered protocol-state sequence, not a narrow uncontrollable race.
* Subsystem rarity penalty not applied. SCTP may be less commonly exposed than TCP, but that is deployment exposure, not concrete evidence for a scoring reduction.
3. Reachability analysis
The strongest supported attacker model is a remote SCTP peer. The commit states that a peer can trigger the same dereference without local help by sending RECONF content in an order where completion handling observes an outbound RECONF request that was published but not yet transmitted. No host-admin-equivalent privilege is required for the remote peer once an SCTP association or reachable SCTP endpoint exists.
A separate local scenario is also described, where an unprivileged process removes an association address and then asks for a stream reset. That supports below-host-admin reachability as well, but the remote peer path is the primary triage driver.
Namespace-scoped privilege is not the relevant boundary for the remote case, so NamespaceScopedPrivilege=NO. Prior host setup is limited to the normal fact that SCTP must be enabled and reachable. No special hardware, firmware, boot mode, or rare physical device prerequisite is established. The trigger is not a hard race.
4. Primitive and severity interpretation
The exact primitive is a NULL pointer dereference of chunk->transport through the RECONF completion path. The bug is an invalid protocol-state match: asoc->strreset_chunk can refer to a RECONF chunk that has not yet been transmitted, so __sctp_packet_append_chunk has not assigned chunk->transport and sctp_outq_flush_ctrl has not armed the reconf timer. Completion then reaches timer_delete on a NULL transport pointer.
This is not an active structured UAF and not fixed stale storage. It is Class C because the demonstrated behavior is crash/DoS from an invalid NULL pointer state without an independently useful corruption primitive. No concrete repeated release/refcount mutation exists. The timer path may release a transport when valid, but here the supplied fault is a NULL dereference before a meaningful stale refcount mutation on a freed object is established.
ImportantCandidate=NO because the evidence supports remote DoS, not memory corruption, boundary bypass, controlled object corruption, or privilege escalation. AutoDowngradeAllowed=YES because no unresolved Class A or Class B primitive remains. However, ManualReview=REQUIRED because the issue is remotely triggerable and can crash the kernel.
5. One-sentence report phrase
A remote SCTP peer can trigger a NULL pointer dereference in RECONF stream reset completion by causing an untransmitted strreset chunk with NULL transport to be matched, leading to a kernel crash and network reachable DoS.
6. Manual review recommendation
MANUAL CHECK REQUIRED
Reason: the bug is remotely triggerable over SCTP and can crash the kernel, even though the established primitive is NULL dereference only and does not show confidentiality, integrity, UAF, or LPE impact.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: sctp: fix NULL deref on untransmitted RECONF completion
Commit: 77ea60f2d24002c308f224db44a4542c466489af
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=77ea60f2d24002c308f224db44a4542c466489af
Commit description:
sctp_process_strreset_outreq(), sctp_process_strreset_addstrm_out() and
sctp_process_strreset_resp() complete a pending stream reconfiguration
request by stopping the reconf timer on the transport it was sent on:
t = asoc->strreset_chunk->transport;
if (timer_delete(&t->reconf_timer))
sctp_transport_put(t);
chunk->transport is assigned by __sctp_packet_append_chunk() when the
chunk is appended to an outbound packet, and sctp_outq_flush_ctrl() arms
the reconf timer at that same point. A request already published in
asoc->strreset_chunk but not yet transmitted has neither, so completing
it dereferences NULL.
Two ways to get there. sctp_send_asconf_del_ip() sets
asoc->src_out_of_asoc_ok without sending anything when the address being
removed is the association's last one, and sctp_outq_flush_ctrl() then
leaves every non-ASCONF control chunk queued; as only
sctp_process_asconf_ack() clears that flag, it persists. An unprivileged
process that removes such an address and then asks for a stream reset
panics the kernel from softirq. A peer needs neither ASCONF nor local
help: sctp_cmd_interpreter() uncorks the outqueue only once the whole
packet has been processed, so a reply built while walking a RECONF chunk
stays untransmitted for the rest of that walk, and one RECONF chunk
carrying [Incoming SSN Reset Request, Outgoing SSN Reset Request,
Response] -- or two RECONF chunks in one packet -- reaches the same
dereference.
KASAN: null-ptr-deref in range [0x00000000000001e8-0x00000000000001ef]
RIP: 0010:timer_delete+0x67/0x110
Call Trace:
<IRQ>
sctp_process_strreset_addstrm_out (net/sctp/stream.c:832)
sctp_sf_do_reconf (net/sctp/sm_statefuns.c:4212)
sctp_do_sm (net/sctp/sm_sideeffect.c:1172)
sctp_assoc_bh_rcv (net/sctp/associola.c:1044)
sctp_rcv (net/sctp/input.c:243)
ip_local_deliver (net/ipv4/ip_input.c:262)
process_backlog (net/core/dev.c:6680)
</IRQ>
A response can only acknowledge a request that was actually sent, so do
not match asoc->strreset_chunk while chunk->transport is NULL. Guarding
the lookup covers all three completion sites.
Fixes: 8105447 ("sctp: implement receiver-side procedures for the Outgoing SSN Reset Request Parameter")
Cc: [email protected]
Reported-by: Xiang Mei <[email protected]>
Suggested-by: Xin Long <[email protected]>
Assisted-by: Claude:claude-opus-5
Signed-off-by: Weiming Shi <[email protected]>
Acked-by: Xin Long <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Paolo Abeni <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
net/sctp/stream.c
net/sctp/sm_statefuns.c
net/sctp/sm_sideeffect.c
net/sctp/associola.c
net/sctp/input.c
net/ipv4/ip_input.c
net/core/dev.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=77ea60f2d24002c308f224db44a4542c466489af
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89477 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89477
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: Not available
The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 7.5
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: 4
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
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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.
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