{"id":"CVE-2026-74621","state":"PUBLISHED","title":"net/sched: act_ct: fix sk_buff leak when the header checks reject a packet","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: act_ct: fix sk_buff leak when the header checks reject a packet\n\ntcf_ct_handle_fragments() runs its header sanity checks before handing\nanything to the defragmentation engine:\n\n\tif (family == NFPROTO_IPV4)\n\t\terr = tcf_ct_ipv4_is_fragment(skb, &frag);\n\telse\n\t\terr = tcf_ct_ipv6_is_fragment(skb, &frag);\n\tif (err || !frag)\n\t\treturn err;\n\ntcf_ct_ipv4_is_fragment() returns -EINVAL or -ENOMEM;\ntcf_ct_ipv6_is_fragment() adds -EPROTO when ipv6_find_hdr() fails. None of\nthem frees or queues the skb, so on that path the caller still owns it.\n\ntcf_ct_act() however funnels every non-zero return into the\nownership-transfer exit:\n\n\terr = tcf_ct_handle_fragments(net, skb, family, p->zone, &defrag);\n\tif (err)\n\t\tgoto out_frag;\n\t...\nout_frag:\n\tif (err != -EINPROGRESS)\n\t\ttcf_action_inc_drop_qstats(&c->common);\n\treturn TC_ACT_CONSUMED;\n\nTC_ACT_CONSUMED means the action took ownership of the skb, so no caller\nfrees it - sch_handle_ingress(), sch_handle_egress() and\ntcf_qevent_handle() all deliberately skip the free for that verdict. The\nskb is therefore orphaned: one sk_buff plus its data buffer is leaked per\nmalformed packet, unbounded. Note the drop counter is already incremented\nfor these errors, so the statistics claim a drop that never happens.\n\nThree different ownership states reach out_frag: today - the skb may be\nqueued by the defrag engine (-EINPROGRESS), already freed by\nnf_ct_handle_fragments(), or still owned by us. Tell the caller which of\nthose it is, and free the packet ourselves in the last case, which\nrestores the TC_ACT_SHOT behaviour that predated the Fixes: commit.\n\nReproduced on v7.2-rc6 with a 54-byte frame carrying a 40-byte IPv6\nheader with nexthdr = 0 (hop-by-hop) and nothing after it, on a\nclsact ingress chain with \"action ct\". kmemleak reports one leaked\n232-byte skbuff_head_cache object plus its 704-byte data buffer per\npacket; with this patch it reports none.","publishedAt":"2026-08-22T15:32:04.990Z","updatedAt":"2026-10-16T19:06:02.607Z","severity":{"score":7.5,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"172ba7d46c202e679f3ccb10264c67416aaeb1c4","status":"affected","lessThan":"b5dbecc2016e1692fd1c2532af9c41ba729cb747","versionType":"git"},{"version":"0b5b831122fc3789fff75be433ba3e4dd7b779d4","status":"affected","lessThan":"23e97d594ddd0153020c506d5041048fbde1beb4","versionType":"git"},{"version":"73f7da5fd124f2cda9161e2e46114915e6e82e97","status":"affected","lessThan":"737873a59905a54ca0d2d127ef882f3f88bf4379","versionType":"git"},{"version":"3f14b377d01d8357eba032b4cabc8c1149b458b6","status":"affected","lessThan":"47d99828591d0fe8be4b9c8992ff3b8e47968db9","versionType":"git"},{"version":"3f14b377d01d8357eba032b4cabc8c1149b458b6","status":"affected","lessThan":"b47bb899e04b5407c5a63fe88d4b6676586a6e84","versionType":"git"},{"version":"3f14b377d01d8357eba032b4cabc8c1149b458b6","status":"affected","lessThan":"439d3e404f9d5e515911cc8132cde198b337c19e","versionType":"git"},{"version":"3f14b377d01d8357eba032b4cabc8c1149b458b6","status":"affected","lessThan":"8a7ed561671aa6a911a2de99e59ef670a4d0b1df","versionType":"git"},{"version":"f5346df0591d10bc948761ca854b1fae6d2ef441","status":"affected","versionType":"git"},{"version":"5.15.148","status":"affected","lessThan":"5.15.217","versionType":"semver"},{"version":"6.1.75","status":"affected","lessThan":"6.1.184","versionType":"semver"},{"version":"6.6.14","status":"affected","lessThan":"6.6.152","versionType":"semver"},{"version":"6.7.2","status":"affected","lessThan":"6.8","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sched/act_ct.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.8","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.8","versionType":"semver"},{"version":"5.15.217","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.184","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.152","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.104","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.45","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.9","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sched/act_ct.c"]}],"references":["https://git.kernel.org/stable/c/b5dbecc2016e1692fd1c2532af9c41ba729cb747","https://git.kernel.org/stable/c/23e97d594ddd0153020c506d5041048fbde1beb4","https://git.kernel.org/stable/c/737873a59905a54ca0d2d127ef882f3f88bf4379","https://git.kernel.org/stable/c/47d99828591d0fe8be4b9c8992ff3b8e47968db9","https://git.kernel.org/stable/c/b47bb899e04b5407c5a63fe88d4b6676586a6e84","https://git.kernel.org/stable/c/439d3e404f9d5e515911cc8132cde198b337c19e","https://git.kernel.org/stable/c/8a7ed561671aa6a911a2de99e59ef670a4d0b1df"],"weaknesses":[],"ingestedAt":"2026-10-29T20:12:58.252Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/74xxx/CVE-2026-74621.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-74621","state":"PUBLISHED","datePublished":"2026-08-22T15:32:04.990Z","dateUpdated":"2026-10-16T19:06:02.607Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-08-15T05:44:03.921Z"},"containers":{"cna":{"title":"net/sched: act_ct: fix sk_buff leak when the header checks reject a packet","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: act_ct: fix sk_buff leak when the header checks reject a packet\n\ntcf_ct_handle_fragments() runs its header sanity checks before handing\nanything to the defragmentation engine:\n\n\tif (family == NFPROTO_IPV4)\n\t\terr = tcf_ct_ipv4_is_fragment(skb, &frag);\n\telse\n\t\terr = tcf_ct_ipv6_is_fragment(skb, &frag);\n\tif (err || !frag)\n\t\treturn err;\n\ntcf_ct_ipv4_is_fragment() returns -EINVAL or -ENOMEM;\ntcf_ct_ipv6_is_fragment() adds -EPROTO when ipv6_find_hdr() fails. None of\nthem frees or queues the skb, so on that path the caller still owns it.\n\ntcf_ct_act() however funnels every non-zero return into the\nownership-transfer exit:\n\n\terr = tcf_ct_handle_fragments(net, skb, family, p->zone, &defrag);\n\tif (err)\n\t\tgoto out_frag;\n\t...\nout_frag:\n\tif (err != -EINPROGRESS)\n\t\ttcf_action_inc_drop_qstats(&c->common);\n\treturn TC_ACT_CONSUMED;\n\nTC_ACT_CONSUMED means the action took ownership of the skb, so no caller\nfrees it - sch_handle_ingress(), sch_handle_egress() and\ntcf_qevent_handle() all deliberately skip the free for that verdict. The\nskb is therefore orphaned: one sk_buff plus its data buffer is leaked per\nmalformed packet, unbounded. Note the drop counter is already incremented\nfor these errors, so the statistics claim a drop that never happens.\n\nThree different ownership states reach out_frag: today - the skb may be\nqueued by the defrag engine (-EINPROGRESS), already freed by\nnf_ct_handle_fragments(), or still owned by us. Tell the caller which of\nthose it is, and free the packet ourselves in the last case, which\nrestores the TC_ACT_SHOT behaviour that predated the Fixes: commit.\n\nReproduced on v7.2-rc6 with a 54-byte frame carrying a 40-byte IPv6\nheader with nexthdr = 0 (hop-by-hop) and nothing after it, on a\nclsact ingress chain with \"action ct\". kmemleak reports one leaked\n232-byte skbuff_head_cache object plus its 704-byte data buffer per\npacket; with this patch it reports none."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"172ba7d46c202e679f3ccb10264c67416aaeb1c4","status":"affected","lessThan":"b5dbecc2016e1692fd1c2532af9c41ba729cb747","versionType":"git"},{"version":"0b5b831122fc3789fff75be433ba3e4dd7b779d4","status":"affected","lessThan":"23e97d594ddd0153020c506d5041048fbde1beb4","versionType":"git"},{"version":"73f7da5fd124f2cda9161e2e46114915e6e82e97","status":"affected","lessThan":"737873a59905a54ca0d2d127ef882f3f88bf4379","versionType":"git"},{"version":"3f14b377d01d8357eba032b4cabc8c1149b458b6","status":"affected","lessThan":"47d99828591d0fe8be4b9c8992ff3b8e47968db9","versionType":"git"},{"version":"3f14b377d01d8357eba032b4cabc8c1149b458b6","status":"affected","lessThan":"b47bb899e04b5407c5a63fe88d4b6676586a6e84","versionType":"git"},{"version":"3f14b377d01d8357eba032b4cabc8c1149b458b6","status":"affected","lessThan":"439d3e404f9d5e515911cc8132cde198b337c19e","versionType":"git"},{"version":"3f14b377d01d8357eba032b4cabc8c1149b458b6","status":"affected","lessThan":"8a7ed561671aa6a911a2de99e59ef670a4d0b1df","versionType":"git"},{"version":"f5346df0591d10bc948761ca854b1fae6d2ef441","status":"affected","versionType":"git"},{"version":"5.15.148","status":"affected","lessThan":"5.15.217","versionType":"semver"},{"version":"6.1.75","status":"affected","lessThan":"6.1.184","versionType":"semver"},{"version":"6.6.14","status":"affected","lessThan":"6.6.152","versionType":"semver"},{"version":"6.7.2","status":"affected","lessThan":"6.8","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sched/act_ct.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.8","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.8","versionType":"semver"},{"version":"5.15.217","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.184","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.152","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.104","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.45","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.9","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sched/act_ct.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/b5dbecc2016e1692fd1c2532af9c41ba729cb747"},{"url":"https://git.kernel.org/stable/c/23e97d594ddd0153020c506d5041048fbde1beb4"},{"url":"https://git.kernel.org/stable/c/737873a59905a54ca0d2d127ef882f3f88bf4379"},{"url":"https://git.kernel.org/stable/c/47d99828591d0fe8be4b9c8992ff3b8e47968db9"},{"url":"https://git.kernel.org/stable/c/b47bb899e04b5407c5a63fe88d4b6676586a6e84"},{"url":"https://git.kernel.org/stable/c/439d3e404f9d5e515911cc8132cde198b337c19e"},{"url":"https://git.kernel.org/stable/c/8a7ed561671aa6a911a2de99e59ef670a4d0b1df"}],"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 - The leak is triggered in tcf_ct_act() on the packet datapath (netif_receive_skb → sch_handle_ingress/egress → tc_run → tcf_classify); on OVN/Kubernetes/SDN gateways and mlx5-offload nodes with act_ct on clsact, a remote peer sends malformed IP packets with no local access required.\nAC:L - The attacker fully controls packet contents; a 54-byte IPv6 frame with nexthdr=0 (hop-by-hop) and no trailing data deterministically makes ipv6_find_hdr() return -EPROTO, leaking one skb per packet without races or uncontrollable layout dependencies.\nPR:N - Installing act_ct requires CAP_NET_ADMIN, but triggering the leak on an already-configured internet-facing or tenant-facing gateway needs no target credentials; a remote attacker only sends crafted malformed IP packets, matching CNA precedent for packet-driven act_ct issues (e.g., CVE-2026-72057).\nUI:N - Exploitation requires only attacker-generated malformed packets reaching a host with act_ct on clsact/ingress or egress; no victim login, mount, or other interactive action is needed beyond normal network traffic processing.\nS:U - The leaked sk_buff objects remain within the host kernel memory domain; this is not a VM escape, sandbox breakout, or IOMMU boundary bypass, only unbounded kernel heap consumption on the affected node.\nC:N - This is a pure sk_buff ownership leak on an error path; skb memory is orphaned, not exposed to the attacker, with no out-of-bounds read, use-after-free, or other disclosure primitive.\nI:N - The flaw only fails to kfree_skb() when header validation rejects a packet; it does not corrupt, overwrite, or modify any memory contents and provides no write or code-execution primitive.\nA:H - Each malformed packet leaks one sk_buff plus its data buffer (~936 bytes); sustained remote flooding causes unbounded kernel memory exhaustion and OOM denial of service, matching CNA precedent for repeatable network-triggered skb leaks (e.g., CVE-2026-52974)."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-25T05:40:45.894Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.15.148","versionEndExcluding":"5.15.217"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.1.75","versionEndExcluding":"6.1.184"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.6.14","versionEndExcluding":"6.6.152"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.8","versionEndExcluding":"6.12.104"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.8","versionEndExcluding":"6.18.45"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.8","versionEndExcluding":"7.1.9"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.8","versionEndExcluding":"7.2"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.7.2"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-74621","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"version":"2.0.3","timestamp":"2026-10-16T19:02:40.438798Z"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-16T19:06:02.607Z"}}]}}}