{ "schema_version": "1.6.1", "id": "RPI-CVE-2026-46099", "modified": "2026-10-09T11:39:44Z", "upstream": [ "CVE-2026-46099" ], "published": "2026-05-27T12:59:23Z", "summary": "net: ipv6: fix NOREF dst use in seg6 and rpl lwtunnels", "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 -> 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.", "severity": [ { "type": "CVSS_V3", "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H" } ], "affected": [ { "package": { "ecosystem": "Raspberry Pi OS:12", "name": "linux" }, "versions": [ "1:6.1.47-1+rpt4" ], "ecosystem_specific": { "binaries": [ { "binary_name": "linux-image-6.1.0-rpi3-rpi-2712", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v6", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v7", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v7l", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v8", "binary_version": "1:6.1.47-1+rpt4" } ] }, "database_specific": { "per_version": { "1:6.1.47-1+rpt4": { "linux_commit": "655fc658a15ae7a6f37103754adb39ba52a9a14e", "upstream_version": "6.1.47", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.1.175", "compiled_filter": false } } } } ], "references": [ { "type": "ADVISORY", "url": "https://www.cve.org/CVERecord?id=CVE-2026-46099" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/51fef5a7c4d160839199e941929456ba21ddf73c" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/b258b849a580285a1692e782ebc902b44c884a71" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/6bd17925bd6866027a6555db17905b9fc073d38d" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/52f9db67f8f35f436366cf4980b4f0a2583d0ef0" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/b778b6d095421619c331fd2d7751143cd5387103" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/9dd5481f960e337b81d7dfe429529495c1c481c0" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/f9c52a6ba9780bd27e0bf4c044fd91c13c778b6e" } ], "database_specific": { "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git", "upstream_modified": "2026-08-05T13:16:28Z", "severity": { "source": "kernel CNA", "cvss_v3_score": 8.1, "cvss_v3_severity": "High", "scenario": "AV:N - The seg6/RPL lwtunnel input handlers run on the IPv6 packet receive/forward path (lwtunnel_input \u2192 seg6_input/rpl_input); a remote attacker sending IPv6 packets matching a configured SRv6/RPL-encap route reaches the vulnerable code.\nAC:H - The UAF manifests only on PREEMPT_RT kernels built without PREEMPT_RT_NEEDS_BH_LOCK (a rare, non-default configuration) and additionally requires winning a tight race against a higher-priority task's concurrent FIB lookup plus a sernum bump on a shared nexthop \u2014 conditions outside the attacker's control.\nPR:N - The triggering packets require no privileges; the SRv6/RPL route configuration is an environmental precondition (CAP_NET_ADMIN to set up), not a privilege the network attacker must hold.\nUI:N - The bug is triggered purely by inbound packet processing in softirq context; no victim interaction is needed.\nS:U - The use-after-free is confined to kernel route/dst objects within the kernel's own security authority; no boundary (VM/IOMMU) is crossed.\nC:H - The freed rt6_info/dst object is read back (rt6_get_cookie/dst dereferences) and can be reallocated with attacker-influenced heap content, enabling kernel memory disclosure.\nI:H - A use-after-free on a route object allows heap-spray reallocation and write/control primitives via the dangling dst that is subsequently used for routing decisions.\nA:H - dst_hold() on the dead object triggers a WARN and the use-after-free of a freed route can cause an oops/panic, crashing the kernel." } } }