net: ipv6: fix NOREF dst use in seg6 and rpl lwtunnels

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Summary

CVECVE-2026-46099
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-05-27 14:17:31 UTC
Updated2026-05-30 11:17:20 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: net: ipv6: fix NOREF dst use in seg6 and rpl lwtunnels seg6_input_core() and rpl_input() call ip6_route_input() which sets a NOREF dst on the skb, then pass it to dst_cache_set_ip6() invoking dst_hold() unconditionally. On PREEMPT_RT, ksoftirqd is preemptible and a higher-priority task can release the underlying pcpu_rt between the lookup and the caching through a concurrent FIB lookup on a shared nexthop. Simplified race sequence: ksoftirqd/X higher-prio task (same CPU X) ----------- -------------------------------- seg6_input_core(,skb)/rpl_input(skb) dst_cache_get() -> miss ip6_route_input(skb) -> ip6_pol_route(,skb,flags) [RT6_LOOKUP_F_DST_NOREF in flags] -> FIB lookup resolves fib6_nh [nhid=N route] -> rt6_make_pcpu_route() [creates pcpu_rt, refcount=1] pcpu_rt->sernum = fib6_sernum [fib6_sernum=W] -> cmpxchg(fib6_nh.rt6i_pcpu, NULL, pcpu_rt) [slot was empty, store succeeds] -> skb_dst_set_noref(skb, dst) [dst is pcpu_rt, refcount still 1] rt_genid_bump_ipv6() -> bumps fib6_sernum [fib6_sernum from W to Z] ip6_route_output() -> ip6_pol_route() -> FIB lookup resolves fib6_nh [nhid=N] -> rt6_get_pcpu_route() pcpu_rt->sernum != fib6_sernum [W <> Z, stale] -> prev = xchg(rt6i_pcpu, NULL) -> dst_release(prev) [prev is pcpu_rt, refcount 1->0, dead] dst = skb_dst(skb) [dst is the dead pcpu_rt] dst_cache_set_ip6(dst) -> dst_hold() on dead dst -> WARN / use-after-free For the race to occur, ksoftirqd must be preemptible (PREEMPT_RT without PREEMPT_RT_NEEDS_BH_LOCK) and a concurrent task must be able to release the pcpu_rt. Shared nexthop objects provide such a path, as two routes pointing to the same nhid share the same fib6_nh and its rt6i_pcpu entry. Fix seg6_input_core() and rpl_input() by calling skb_dst_force() after ip6_route_input() to force the NOREF dst into a refcounted one before caching. The output path is not affected as ip6_route_output() already returns a refcounted dst.

Risk And Classification

Primary CVSS: v3.1 8.1 HIGH from 416baaa9-dc9f-4396-8d5f-8c081fb06d67

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS: 0.000180000 probability, percentile 0.051640000 (date 2026-05-29)

VersionSourceTypeScoreSeverityVector
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary8.1HIGHCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
3.1CNADECLARED8.1HIGHCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected af4a2209b1344939eaac11f269c261d347cbc3ee 6bd17925bd6866027a6555db17905b9fc073d38d git Not specified
CNA Linux Linux affected af4a2209b1344939eaac11f269c261d347cbc3ee 52f9db67f8f35f436366cf4980b4f0a2583d0ef0 git Not specified
CNA Linux Linux affected af4a2209b1344939eaac11f269c261d347cbc3ee b778b6d095421619c331fd2d7751143cd5387103 git Not specified
CNA Linux Linux affected af4a2209b1344939eaac11f269c261d347cbc3ee 9dd5481f960e337b81d7dfe429529495c1c481c0 git Not specified
CNA Linux Linux affected af4a2209b1344939eaac11f269c261d347cbc3ee f9c52a6ba9780bd27e0bf4c044fd91c13c778b6e git Not specified
CNA Linux Linux affected 4.12 Not specified
CNA Linux Linux unaffected 4.12 semver Not specified
CNA Linux Linux unaffected 6.6.140 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.86 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.27 6.18.* semver Not specified
CNA Linux Linux unaffected 7.0.4 7.0.* semver Not specified
CNA Linux Linux unaffected 7.1-rc2 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/9dd5481f960e337b81d7dfe429529495c1c481c0 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/b778b6d095421619c331fd2d7751143cd5387103 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/52f9db67f8f35f436366cf4980b4f0a2583d0ef0 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/f9c52a6ba9780bd27e0bf4c044fd91c13c778b6e 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/6bd17925bd6866027a6555db17905b9fc073d38d 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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