* [CVE-2026-93226][LOW] ipv6: use RCU iterator to dump route exceptions
@ 2026-09-24 18:02 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-24 18:02 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-93226
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: ipv6: use RCU iterator to dump route exceptions
Commit: dffbfb3117138e8e0e09d05f507bd36ca1f696e5
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dffbfb3117138e8e0e09d05f507bd36ca1f696e5
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93226
Analysis date: Thu, 24 Sep 2026 14:02:50 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-93226 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93226
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: LOW
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-2026-93226 LOW https://www.kernelcve.org/list/?q=CVE-2026-93226 CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:N';CWE-362;CWE-366;BEST CVSS score: '0';DESCR 'A race exists in IPv6 route exception dumping because rt6_nh_dump_exceptions reads an RCU protected hlist with a non RCU iterator while rt6_insert_exception can concurrently add an exception entry. A local process performing a netlink route dump can race with PMTU exception insertion, producing an RCU access ordering violation reported by KCSAN. For the CVSS the PR:L metric is used because a local process must issue the route dump operation even if network traffic can contribute to exception creation. The patch context does not show a use after free, out of bounds access, invalid write, information leak, kernel crash, or privilege escalation. Impact is limited to a correctness race and potentially inconsistent route dump output. The issue is not directly network reachable as an exploitable vulnerability.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0) YES REMOTE KASAN RACE NETWORK HARDWARE IPV6 DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=0
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 0
* Conservative score: 0
* Raw paranoid score: 0
* Paranoid score: 0
* Final recommended bucket: **Ordinary Moderate**::
No floor or cap was applied.
2. Signal breakdown
* +0 RCU iterator correctness race. The patch replaces a non RCU hlist iterator with hlist_for_each_entry_rcu while the caller already holds rcu_read_lock.
* +0 No real UAF. The supplied concurrent writer adds an entry using hlist_add_head_rcu. No removal, free, retired referenced object, or stale post-lifetime dereference is established.
* +0 No invalid write, out of bounds access, refcount mutation, controlled replacement, callback use, disclosure, authorization bypass, kernel crash, or privilege escalation is established.
* +0 No direct remote exploitability. Incoming ICMPv6 processing may cause PMTU exception insertion, but an attacker also needs a concurrent local route dump and the demonstrated result is only an RCU access ordering race.
* +0 No reliable DoS. KCSAN reports a data race, not an Oops, panic, soft lockup, or route-table corruption.
* No race penalty was applied. The race does not receive a score and no evidence establishes a security-relevant timing primitive.
* No confidentiality or integrity points were awarded. An inconsistent route dump is not a demonstrated disclosure or unauthorized state modification.
3. Reachability analysis
A local process can normally request IPv6 route dumps through rtnetlink without host-admin-equivalent privilege, so HostAdminRequired is NO. Concurrent PMTU exception insertion can occur during IPv6 error processing, including ICMPv6 processing, but that does not itself provide a remotely exploitable vulnerability.
No capability-gated setup is shown. Namespace-scoped privilege is not relevant because the route dump operation itself does not require a delegated capability for the demonstrated race. No special hardware, boot option, privileged device setup, or uncommon subsystem configuration is required beyond IPv6 routing activity.
4. Primitive and severity interpretation
The exact issue is an RCU access discipline violation. rt6_nh_dump_exceptions traverses an RCU protected hlist with hlist_for_each_entry instead of hlist_for_each_entry_rcu while rt6_insert_exception may concurrently publish a new element through hlist_add_head_rcu.
This is not an active-object lifetime violation. The supplied evidence shows insertion of a new exception entry, not removal or freeing of an entry that is subsequently dereferenced. Therefore there is no demonstrated stale-object use, UAF, double release, refcount corruption, or meaningful post-free mutation.
The primitive is NONE. The demonstrated consequence is a KCSAN data-race report and potentially inconsistent route-dump visibility. A crash, memory corruption, information disclosure, privilege escalation, or network-triggerable security impact would be speculative and is not supported by the patch. ImportantCandidate is NO and AutoDowngradeAllowed is YES because no unresolved concrete security primitive remains.
5. One-sentence report phrase
An IPv6 route exception dump used a non RCU hlist iterator while exception entries could be concurrently added through RCU, causing a KCSAN reported race without a demonstrated memory safety or security impact.
6. Manual review recommendation
NO MANUAL CHECK NEEDED
The patch fixes RCU iterator semantics for concurrent list insertion, but the supplied code and report establish neither object lifetime loss nor a crash or corruption primitive.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: ipv6: use RCU iterator to dump route exceptions
Commit: dffbfb3117138e8e0e09d05f507bd36ca1f696e5
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dffbfb3117138e8e0e09d05f507bd36ca1f696e5
Commit description:
rt6_nh_dump_exceptions() uses hlist_for_each_entry() to iterate over
RCU-protected exception lists. The caller holds rcu_read_lock(), but does
not hold rt6_exception_lock, so rt6_insert_exception() can concurrently
add an entry with hlist_add_head_rcu().
KCSAN reports this race (irrelevant details omitted):
==================================================================
BUG: KCSAN: data-race in rt6_insert_exception / rt6_nh_dump_exceptions
write (marked) to 0xffff8a7c44c59620 of 8 bytes by interrupt on cpu 5:
rt6_insert_exception+0x3bb/0x760
__ip6_rt_update_pmtu+0x4fe/0x750
ip6_sk_update_pmtu+0x19a/0x3b0
udpv6_err+0x3ff/0x800
icmpv6_notify+0x1e1/0x440
icmpv6_rcv+0x8c0/0xab0
ip6_protocol_deliver_rcu+0x616/0x840
ip6_input_finish+0xb9/0x160
...
entry_SYSCALL_64_after_hwframe+0x77/0x7f
read to 0xffff8a7c44c59620 of 8 bytes by task 549 on cpu 14:
rt6_nh_dump_exceptions+0xb3/0x260
rt6_dump_route+0x53e/0x5f0
fib6_dump_node+0x6d/0xf0
fib6_walk_continue+0x290/0x2d0
fib6_dump_table+0x28d/0x360
inet6_dump_fib+0x37d/0x620
rtnl_dumpit+0x7b/0xd0
netlink_dump+0x3ae/0x7e0
...
entry_SYSCALL_64_after_hwframe+0x77/0x7f
4 locks held by dumper/549:
...
#1: (rcu_read_lock){....}-{1:3}, at: inet6_dump_fib+0x88/0x620
#2: (&tb->tb6_lock){+.-.}-{3:3}, at: fib6_dump_table+0x1e9/0x360
#3: (rcu_read_lock){....}-{1:3}, at: rt6_dump_route+0x483/0x5f0
value changed: 0xffff8a7c44e05700 -> 0xffff8a7c45d60100
Reported by Kernel Concurrency Sanitizer on:
CPU: 14 UID: 0 PID: 549 Comm: dumper Not tainted
7.2.0-rc7-virtme #38 PREEMPT(lazy)
...
Use hlist_for_each_entry_rcu() to safely iterate over the exception list.
Fixes: 1e47b48 ("ipv6: Dump route exceptions if requested")
Cc: [email protected]
Signed-off-by: Yuyang Huang <[email protected]>
Reviewed-by: Stefano Brivio <[email protected]>
Reviewed-by: Ido Schimmel <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: David S. Miller <[email protected]>
Signed-off-by: Jakub Kicinski <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
net/ipv6/route.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=dffbfb3117138e8e0e09d05f507bd36ca1f696e5
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-93226 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93226
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:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:N
The Best / paranoid CVSS score: 0
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: 0
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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW
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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