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VulnerabilityPublished Updated

CVE-2026-46099: Linux kernel · net: ipv6: fix NOREF dst use in seg6 and rpl lwtunnels

Affects Linux kernelSource CVE Database V5

0

Not known to be exploited · CVSS 8.1 High · fixed in f9c52a6ba9780bd27e0bf4c044fd91c13c778b6e : patch Linux kernel soon.

Data as of 26 Oct 2026, 14:18 UTC

CVSS 3.1 base score
8.1High
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.2% chance of exploitation in 30 days – higher than 21% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CISA SSVC
Exploitation
No evidence of active exploitation and no public proof of concept
Automatable
Attackers cannot reliably automate steps 1–4 of the kill chain
Technical impact
Total control over the software or total information disclosure

CISA SSVC assessment, 2026-10-16.

Patch
Available – fixed in f9c52a6ba9780bd27e0bf4c044fd91c13c778b6e, b778b6d095421619c331fd2d7751143cd5387103, b258b849a580285a1692e782ebc902b44c884a71 +4
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 27 May 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

ProductAffectedFixed in
LinuxLinuxAffected
  • ≥ af4a2209b1344939eaac11f269c261d347cbc3ee, < f9c52a6ba9780bd27e0bf4c044fd91c13c778b6e
Fixed in
  • f9c52a6ba9780bd27e0bf4c044fd91c13c778b6e
LinuxLinuxAffected
  • ≥ af4a2209b1344939eaac11f269c261d347cbc3ee, < b778b6d095421619c331fd2d7751143cd5387103
Fixed in
  • b778b6d095421619c331fd2d7751143cd5387103
LinuxLinuxAffected
  • ≥ af4a2209b1344939eaac11f269c261d347cbc3ee, < b258b849a580285a1692e782ebc902b44c884a71
Fixed in
  • b258b849a580285a1692e782ebc902b44c884a71
LinuxLinuxAffected
  • ≥ af4a2209b1344939eaac11f269c261d347cbc3ee, < 52f9db67f8f35f436366cf4980b4f0a2583d0ef0
Fixed in
  • 52f9db67f8f35f436366cf4980b4f0a2583d0ef0
LinuxLinuxAffected
  • ≥ af4a2209b1344939eaac11f269c261d347cbc3ee, < 51fef5a7c4d160839199e941929456ba21ddf73c
Fixed in
  • 51fef5a7c4d160839199e941929456ba21ddf73c
LinuxLinuxAffected
  • ≥ af4a2209b1344939eaac11f269c261d347cbc3ee, < 9dd5481f960e337b81d7dfe429529495c1c481c0
Fixed in
  • 9dd5481f960e337b81d7dfe429529495c1c481c0

Description

In 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.

References

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