{"id":"CVE-2026-46099","revision":"ad8373ba75d94b89894d4664943f402a","records":[{"revision":"ad8373ba75d94b89894d4664943f402a","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-46099","aliases":[],"title":"net: ipv6: fix NOREF dst use in seg6 and rpl lwtunnels","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: ipv6: fix NOREF dst use in seg6 and rpl lwtunnels\n\nseg6_input_core() and rpl_input() call ip6_route_input() which sets a\nNOREF dst on the skb, then pass it to dst_cache_set_ip6() invoking\ndst_hold() unconditionally.\nOn PREEMPT_RT, ksoftirqd is preemptible and a higher-priority task can\nrelease the underlying pcpu_rt between the lookup and the caching\nthrough a concurrent FIB lookup on a shared nexthop.\nSimplified race sequence:\n\n  ksoftirqd/X                       higher-prio task (same CPU X)\n  -----------                       --------------------------------\n  seg6_input_core(,skb)/rpl_input(skb)\n    dst_cache_get()\n      -> miss\n    ip6_route_input(skb)\n      -> ip6_pol_route(,skb,flags)\n         [RT6_LOOKUP_F_DST_NOREF in flags]\n        -> FIB lookup resolves fib6_nh\n           [nhid=N route]\n        -> rt6_make_pcpu_route()\n           [creates pcpu_rt, refcount=1]\n             pcpu_rt->sernum = fib6_sernum\n             [fib6_sernum=W]\n           -> cmpxchg(fib6_nh.rt6i_pcpu,\n                      NULL, pcpu_rt)\n              [slot was empty, store succeeds]\n      -> skb_dst_set_noref(skb, dst)\n         [dst is pcpu_rt, refcount still 1]\n\n                                    rt_genid_bump_ipv6()\n                                      -> bumps fib6_sernum\n                                         [fib6_sernum from W to Z]\n                                    ip6_route_output()\n                                      -> ip6_pol_route()\n                                        -> FIB lookup resolves fib6_nh\n                                           [nhid=N]\n                                        -> rt6_get_pcpu_route()\n                                             pcpu_rt->sernum != fib6_sernum\n                                             [W <> Z, stale]\n                                          -> prev = xchg(rt6i_pcpu, NULL)\n                                          -> dst_release(prev)\n                                             [prev is pcpu_rt,\n                                              refcount 1->0, dead]\n\n    dst = skb_dst(skb)\n    [dst is the dead pcpu_rt]\n    dst_cache_set_ip6(dst)\n      -> dst_hold() on dead dst\n      -> WARN / use-after-free\n\nFor the race to occur, ksoftirqd must be preemptible (PREEMPT_RT without\nPREEMPT_RT_NEEDS_BH_LOCK) and a concurrent task must be able to release\nthe pcpu_rt. Shared nexthop objects provide such a path, as two routes\npointing to the same nhid share the same fib6_nh and its rt6i_pcpu\nentry.\n\nFix seg6_input_core() and rpl_input() by calling skb_dst_force() after\nip6_route_input() to force the NOREF dst into a refcounted one before\ncaching.\nThe output path is not affected as ip6_route_output() already returns a\nrefcounted dst.","state":0,"publishedAt":"2026-05-27T12:59:04.628+00:00","modifiedAt":"2026-10-19T19:26:43.421+00:00","affected":[{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"product\": \"Linux\",\n                    \"vendor\": \"Linux\",\n                    \"defaultStatus\": \"unaffected\",\n                    \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n                    \"programFiles\": [\n                        \"net/ipv6/rpl_iptunnel.c\",\n                        \"net/ipv6/seg6_iptunnel.c\"\n                    ],\n                    \"versions\": [\n                        {\n                            \"version\": \"af4a2209b1344939eaac11f269c261d347cbc3ee\",\n                            \"lessThan\": \"51fef5a7c4d160839199e941929456ba21ddf73c\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"af4a2209b1344939eaac11f269c261d347cbc3ee\",\n                            \"lessThan\": \"b258b849a580285a1692e782ebc902b44c884a71\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"af4a2209b1344939eaac11f269c261d347cbc3ee\",\n                            \"lessThan\": \"6bd17925bd6866027a6555db17905b9fc073d38d\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"af4a2209b1344939eaac11f269c261d347cbc3ee\",\n                            \"lessThan\": \"52f9db67f8f35f436366cf4980b4f0a2583d0ef0\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"af4a2209b1344939eaac11f269c261d347cbc3ee\",\n                            \"lessThan\": \"b778b6d095421619c331fd2d7751143cd5387103\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"af4a2209b1344939eaac11f269c261d347cbc3ee\",\n                            \"lessThan\": \"9dd5481f960e337b81d7dfe429529495c1c481c0\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"af4a2209b1344939eaac11f269c261d347cbc3ee\",\n                            \"lessThan\": \"f9c52a6ba9780bd27e0bf4c044fd91c13c778b6e\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        }\n                    ]\n                }"},{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"product\": \"Linux\",\n                    \"vendor\": \"Linux\",\n                    \"defaultStatus\": \"affected\",\n                    \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n                    \"programFiles\": [\n                        \"net/ipv6/rpl_iptunnel.c\",\n                        \"net/ipv6/seg6_iptunnel.c\"\n                    ],\n                    \"versions\": [\n                        {\n                            \"version\": \"4.12\",\n                            \"status\": \"affected\"\n                        },\n                        {\n                            \"version\": \"0\",\n                            \"lessThan\": \"4.12\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"5.15.209\",\n                            \"lessThanOrEqual\": \"5.15.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.1.175\",\n                            \"lessThanOrEqual\": \"6.1.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.6.140\",\n                            \"lessThanOrEqual\": \"6.6.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.12.86\",\n                            \"lessThanOrEqual\": \"6.12.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.18.27\",\n                            \"lessThanOrEqual\": \"6.18.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"7.0.4\",\n                            \"lessThanOrEqual\": \"7.0.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"7.1\",\n                            \"lessThanOrEqual\": \"*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"original_commit_for_fix\"\n                        }\n                    ]\n                }"}],"metrics":[{"system":"CVSS 3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H","score":8.1,"severity":"HIGH"}],"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"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-46099","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-46099","identifiers":["CVE-2026-46099"]},"retained":false,"historicalAffected":[]}],"coverage":[]}