{"id":"AZL-88526","summary":"CVE-2026-46099 affecting package kernel for versions less than 6.6.141.1-1","details":"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      -\u003e miss\n    ip6_route_input(skb)\n      -\u003e ip6_pol_route(,skb,flags)\n         [RT6_LOOKUP_F_DST_NOREF in flags]\n        -\u003e FIB lookup resolves fib6_nh\n           [nhid=N route]\n        -\u003e rt6_make_pcpu_route()\n           [creates pcpu_rt, refcount=1]\n             pcpu_rt-\u003esernum = fib6_sernum\n             [fib6_sernum=W]\n           -\u003e cmpxchg(fib6_nh.rt6i_pcpu,\n                      NULL, pcpu_rt)\n              [slot was empty, store succeeds]\n      -\u003e skb_dst_set_noref(skb, dst)\n         [dst is pcpu_rt, refcount still 1]\n\n                                    rt_genid_bump_ipv6()\n                                      -\u003e bumps fib6_sernum\n                                         [fib6_sernum from W to Z]\n                                    ip6_route_output()\n                                      -\u003e ip6_pol_route()\n                                        -\u003e FIB lookup resolves fib6_nh\n                                           [nhid=N]\n                                        -\u003e rt6_get_pcpu_route()\n                                             pcpu_rt-\u003esernum != fib6_sernum\n                                             [W \u003c\u003e Z, stale]\n                                          -\u003e prev = xchg(rt6i_pcpu, NULL)\n                                          -\u003e dst_release(prev)\n                                             [prev is pcpu_rt,\n                                              refcount 1-\u003e0, dead]\n\n    dst = skb_dst(skb)\n    [dst is the dead pcpu_rt]\n    dst_cache_set_ip6(dst)\n      -\u003e dst_hold() on dead dst\n      -\u003e 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.","modified":"2026-08-28T17:47:38.992492690Z","published":"2026-05-27T14:17:31Z","upstream":["CVE-2026-46099"],"references":[{"type":"WEB","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-46099"}],"affected":[{"package":{"name":"kernel","ecosystem":"Azure Linux:3","purl":"pkg:rpm/azure-linux/kernel"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.6.141.1-1"}]}],"database_specific":{"source":"https://github.com/microsoft/AzureLinuxVulnerabilityData/blob/main/osv/AZL-88526.json"}}],"schema_version":"1.9.0"}