Skip to main content
cve.nowby Sazabi
← All vulnerabilities
CVE-2026-46099

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

Published
Last modified
published
Not listed in CISA KEV
Fix
Fixed in 5.15.209, 6.1.175, 6.6.140, 6.12.86, 6.18.27, and 1 more
None on Exploit-DB, Metasploit or GitHub
  • Exploitation: none
  • Automatable: no
  • Technical impact: total

Summary

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.

Timeline

  1. CVE published
  2. CISA SSVC assessment

    Exploitation: none · Automatable: no · Technical impact: total

  3. Record last updated

Affected versions

  • Linux Linux

    From af4a2209b1344939eaac11f269c261d347cbc3ee · fixed in 51fef5a7c4d160839199e941929456ba21ddf73c; From af4a2209b1344939eaac11f269c261d347cbc3ee · fixed in b258b849a580285a1692e782ebc902b44c884a71; From af4a2209b1344939eaac11f269c261d347cbc3ee · fixed in 6bd17925bd6866027a6555db17905b9fc073d38d; From af4a2209b1344939eaac11f269c261d347cbc3ee · fixed in 52f9db67f8f35f436366cf4980b4f0a2583d0ef0; From af4a2209b1344939eaac11f269c261d347cbc3ee · fixed in b778b6d095421619c331fd2d7751143cd5387103; From af4a2209b1344939eaac11f269c261d347cbc3ee · fixed in 9dd5481f960e337b81d7dfe429529495c1c481c0; From af4a2209b1344939eaac11f269c261d347cbc3ee · fixed in f9c52a6ba9780bd27e0bf4c044fd91c13c778b6e

  • Linux Linux

    4.12

  • KernelLinux

    From 4.12.0 · fixed in 5.15.209; From 5.16.0 · fixed in 6.1.175; From 6.2.0 · fixed in 6.6.140; From 6.7.0 · fixed in 6.12.86; From 6.13.0 · fixed in 6.18.27; From 6.19.0 · fixed in 7.0.4

References 7

git.kernel.org