{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2021-47515","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","state":"PUBLISHED","assignerShortName":"Linux","dateReserved":"2024-05-24T15:02:54.824Z","datePublished":"2024-05-24T15:09:29.334Z","dateUpdated":"2026-08-05T08:48:12.387Z"},"containers":{"cna":{"providerMetadata":{"orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux","dateUpdated":"2026-08-05T08:48:12.387Z"},"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nseg6: fix the iif in the IPv6 socket control block\n\nWhen an IPv4 packet is received, the ip_rcv_core(...) sets the receiving\ninterface index into the IPv4 socket control block (v5.16-rc4,\nnet/ipv4/ip_input.c line 510):\n\n    IPCB(skb)->iif = skb->skb_iif;\n\nIf that IPv4 packet is meant to be encapsulated in an outer IPv6+SRH\nheader, the seg6_do_srh_encap(...) performs the required encapsulation.\nIn this case, the seg6_do_srh_encap function clears the IPv6 socket control\nblock (v5.16-rc4 net/ipv6/seg6_iptunnel.c line 163):\n\n    memset(IP6CB(skb), 0, sizeof(*IP6CB(skb)));\n\nThe memset(...) was introduced in commit ef489749aae5 (\"ipv6: sr: clear\nIP6CB(skb) on SRH ip4ip6 encapsulation\") a long time ago (2019-01-29).\n\nSince the IPv6 socket control block and the IPv4 socket control block share\nthe same memory area (skb->cb), the receiving interface index info is lost\n(IP6CB(skb)->iif is set to zero).\n\nAs a side effect, that condition triggers a NULL pointer dereference if\ncommit 0857d6f8c759 (\"ipv6: When forwarding count rx stats on the orig\nnetdev\") is applied.\n\nTo fix that issue, we set the IP6CB(skb)->iif with the index of the\nreceiving interface once again."}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","baseScore":7.5,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:N - On an SRv6 PE/router with ip4ip6 encap routes, a remote IPv4 packet is received, encapsulated in seg6_do_srh_encap(), then forwarded via ip6_forward(), so the crash is reachable over the network without local access.\nAC:L - Once SRv6 encap for IPv4 is configured (the intended deployment for this code), any matching IPv4 packet reliably clears IP6CB(skb)->iif and hits the NULL dereference; no race or attacker-uncontrollable memory layout is required.\nPR:N - Triggering requires only sending unauthenticated IPv4 packets that match an already-configured SRv6 encap route; the attacker needs no account or capability on the target.\nUI:N - Packet processing runs entirely in the kernel receive/forward path with no victim user action beyond the router already having SRv6 encap configured.\nS:U - The NULL dereference oopses the same host kernel that performs forwarding and does not cross a VM, IOMMU, or other security-authority boundary.\nC:N - This is a pure NULL pointer dereference of idev in ip6_forward() after iif is cleared to zero, with no OOB read, UAF, or other information-disclosure primitive.\nI:N - The fault is a straight NULL dereference of idev->cnf.disable_policy with no write primitive, type confusion, or memory corruption that could alter kernel state or hijack control flow.\nA:H - Dereferencing the NULL inet6_dev pointer in ip6_forward() causes a kernel oops/panic and can be re-triggered at will by remote packets, taking down the system."}]}],"affected":[{"product":"Linux","vendor":"Linux","defaultStatus":"unaffected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv6/seg6_iptunnel.c"],"versions":[{"version":"c630ec8bdadae9d557b1ceb9d6c06e149108a0d4","lessThan":"b16d412e5f79734033df04e97d7ea2f50a8e9fe3","status":"affected","versionType":"git"},{"version":"2f704348c93ff8119e642dae6a72327f90b82810","lessThan":"6431e71093f3da586a00c6d931481ffb0dc2db0e","status":"affected","versionType":"git"},{"version":"ef489749aae508e6f17886775c075f12ff919fb1","lessThan":"ef8804e47c0a44ae106ead1740408af5ea6c6ee9","status":"affected","versionType":"git"},{"version":"ef489749aae508e6f17886775c075f12ff919fb1","lessThan":"666521b3852d2b2f52d570f9122b1e4b50d96831","status":"affected","versionType":"git"},{"version":"ef489749aae508e6f17886775c075f12ff919fb1","lessThan":"98adb2bbfa407c9290bda299d4c6f7a1c4ebd5e1","status":"affected","versionType":"git"},{"version":"ef489749aae508e6f17886775c075f12ff919fb1","lessThan":"ae68d93354e5bf5191ee673982251864ea24dd5c","status":"affected","versionType":"git"},{"version":"b71b7e0280f47b4ac633fbfd153423814ea87810","status":"affected","versionType":"git"},{"version":"4.14.98","lessThan":"4.14.258","status":"affected","versionType":"semver"},{"version":"4.19.20","lessThan":"4.19.221","status":"affected","versionType":"semver"},{"version":"4.20.7","lessThan":"4.21","status":"affected","versionType":"semver"}]},{"product":"Linux","vendor":"Linux","defaultStatus":"affected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv6/seg6_iptunnel.c"],"versions":[{"version":"5.0","status":"affected"},{"version":"0","lessThan":"5.0","status":"unaffected","versionType":"semver"},{"version":"4.14.258","lessThanOrEqual":"4.14.*","status":"unaffected","versionType":"semver"},{"version":"4.19.221","lessThanOrEqual":"4.19.*","status":"unaffected","versionType":"semver"},{"version":"5.4.165","lessThanOrEqual":"5.4.*","status":"unaffected","versionType":"semver"},{"version":"5.10.85","lessThanOrEqual":"5.10.*","status":"unaffected","versionType":"semver"},{"version":"5.15.8","lessThanOrEqual":"5.15.*","status":"unaffected","versionType":"semver"},{"version":"5.16","lessThanOrEqual":"*","status":"unaffected","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.14.98","versionEndExcluding":"4.14.258"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19.20","versionEndExcluding":"4.19.221"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.0","versionEndExcluding":"5.4.165"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.0","versionEndExcluding":"5.10.85"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.0","versionEndExcluding":"5.15.8"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.0","versionEndExcluding":"5.16"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.20.7"}]}]}],"references":[{"url":"https://git.kernel.org/stable/c/b16d412e5f79734033df04e97d7ea2f50a8e9fe3"},{"url":"https://git.kernel.org/stable/c/6431e71093f3da586a00c6d931481ffb0dc2db0e"},{"url":"https://git.kernel.org/stable/c/ef8804e47c0a44ae106ead1740408af5ea6c6ee9"},{"url":"https://git.kernel.org/stable/c/666521b3852d2b2f52d570f9122b1e4b50d96831"},{"url":"https://git.kernel.org/stable/c/98adb2bbfa407c9290bda299d4c6f7a1c4ebd5e1"},{"url":"https://git.kernel.org/stable/c/ae68d93354e5bf5191ee673982251864ea24dd5c"}],"title":"seg6: 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