{"id":"CVE-2026-72404","state":"PUBLISHED","title":"tipc: fix UAF in cleanup_bearer() due to premature dst_cache_destroy()","description":"In the Linux kernel, the following vulnerability has been resolved:\n\ntipc: fix UAF in cleanup_bearer() due to premature dst_cache_destroy()\n\nTIPC UDP media bearer teardown calls dst_cache_destroy() on its\nreplicast caches before calling synchronize_net() to wait for\nconcurrent RCU readers (transmitters) to finish:\n\nstatic void cleanup_bearer(struct work_struct *work)\n{\n...\n\tlist_for_each_entry_safe(rcast, tmp, &ub->rcast.list, list) {\n\t\tdst_cache_destroy(&rcast->dst_cache);\n\t\tlist_del_rcu(&rcast->list);\n\t\tkfree_rcu(rcast, rcu);\n\t}\n...\n\tdst_cache_destroy(&ub->rcast.dst_cache);\n\tudp_tunnel_sock_release(ub->sk);\n\tsynchronize_net();\n...\n}\n\nThis is highly buggy because dst_cache_destroy() immediately frees the\nper-CPU cache memory (free_percpu()) and releases the cached dst\nentries without any synchronization.\n\nIf a concurrent transmitter (e.g., tipc_udp_xmit()) is running on another\nCPU under RCU protection, it can call dst_cache_get() concurrently,\nleading to:\n1. Use-After-Free on the per-CPU cache pointer itself (crash).\n2. \"rcuref - imbalanced put()\" warning if it attempts to release a\n   dst that was concurrently released by dst_cache_destroy().\n\nFurthermore, calling kfree(ub) immediately after synchronize_net() without\nclosing the socket first (or waiting after closing it) leaves a window\nwhere a concurrent receiver (tipc_udp_recv()) could start after\nsynchronize_net(), access ub, and suffer a UAF when kfree(ub) runs.\n\nTo fix this, we must defer dst_cache_destroy() and kfree(ub) until after\nwe have ensured that no more readers can see the bearer/socket and all\nexisting readers have finished:\n\n1. Defer rcast entry destruction (both dst_cache_destroy() and kfree())\n   to an RCU callback using call_rcu_hurry().\n   Using call_rcu_hurry() ensures the dst entries are released quickly.\n\n2. Release the bearer socket using udp_tunnel_sock_release() (stops\n   new receive readers).\n\n3. Call synchronize_net() to wait for all outstanding RCU readers\n   (both transmit and receive) to finish.\n\n4. Now that it is safe, call dst_cache_destroy() on the main bearer\n   cache, and free ub.\n\nNote: 3) and 4) can be changed later in net-next to also use\ncall_rcu_hurry() and get rid of the synchronize_net() latency.","publishedAt":"2026-08-15T05:56:28.124Z","updatedAt":"2026-10-30T12:29:17.840Z","severity":{"score":7.8,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"e9c1a793210f29f32ee4cf048e04d7d9bb3221cc","status":"affected","lessThan":"5a66ca574eee958123ee9d2822683964d42d656a","versionType":"git"},{"version":"e9c1a793210f29f32ee4cf048e04d7d9bb3221cc","status":"affected","lessThan":"6aeb4ba4fb098199e13723cfd04d9a749741f731","versionType":"git"},{"version":"e9c1a793210f29f32ee4cf048e04d7d9bb3221cc","status":"affected","lessThan":"6b0e29f7662c237e717f35dad746efe94715d0da","versionType":"git"},{"version":"e9c1a793210f29f32ee4cf048e04d7d9bb3221cc","status":"affected","lessThan":"3827ff67f9fbecd1086e33d23693ef6a1a9c6c38","versionType":"git"},{"version":"e9c1a793210f29f32ee4cf048e04d7d9bb3221cc","status":"affected","lessThan":"1c8393eefa3cadf4ca0b61119ad1321aa32d3c8c","versionType":"git"},{"version":"e9c1a793210f29f32ee4cf048e04d7d9bb3221cc","status":"affected","lessThan":"7116764ca53ff529335d7ab7c364a69f094b23a5","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/tipc/udp_media.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.3","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.3","versionType":"semver"},{"version":"6.1.191","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.160","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.114","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.57","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.5","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/tipc/udp_media.c"]}],"references":["https://git.kernel.org/stable/c/5a66ca574eee958123ee9d2822683964d42d656a","https://git.kernel.org/stable/c/6aeb4ba4fb098199e13723cfd04d9a749741f731","https://git.kernel.org/stable/c/6b0e29f7662c237e717f35dad746efe94715d0da","https://git.kernel.org/stable/c/3827ff67f9fbecd1086e33d23693ef6a1a9c6c38","https://git.kernel.org/stable/c/1c8393eefa3cadf4ca0b61119ad1321aa32d3c8c","https://git.kernel.org/stable/c/7116764ca53ff529335d7ab7c364a69f094b23a5"],"weaknesses":[],"ingestedAt":"2026-10-30T12:48:04.825Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/72xxx/CVE-2026-72404.json","commit":"1f312381e38164a43607eebab851b151dd16861e","baselineCommit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-72404","state":"PUBLISHED","datePublished":"2026-08-15T05:56:28.124Z","dateUpdated":"2026-10-30T12:29:17.840Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-08-09T03:40:39.925Z"},"containers":{"cna":{"title":"tipc: fix UAF in cleanup_bearer() due to premature dst_cache_destroy()","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\ntipc: fix UAF in cleanup_bearer() due to premature dst_cache_destroy()\n\nTIPC UDP media bearer teardown calls dst_cache_destroy() on its\nreplicast caches before calling synchronize_net() to wait for\nconcurrent RCU readers (transmitters) to finish:\n\nstatic void cleanup_bearer(struct work_struct *work)\n{\n...\n\tlist_for_each_entry_safe(rcast, tmp, &ub->rcast.list, list) {\n\t\tdst_cache_destroy(&rcast->dst_cache);\n\t\tlist_del_rcu(&rcast->list);\n\t\tkfree_rcu(rcast, rcu);\n\t}\n...\n\tdst_cache_destroy(&ub->rcast.dst_cache);\n\tudp_tunnel_sock_release(ub->sk);\n\tsynchronize_net();\n...\n}\n\nThis is highly buggy because dst_cache_destroy() immediately frees the\nper-CPU cache memory (free_percpu()) and releases the cached dst\nentries without any synchronization.\n\nIf a concurrent transmitter (e.g., tipc_udp_xmit()) is running on another\nCPU under RCU protection, it can call dst_cache_get() concurrently,\nleading to:\n1. Use-After-Free on the per-CPU cache pointer itself (crash).\n2. \"rcuref - imbalanced put()\" warning if it attempts to release a\n   dst that was concurrently released by dst_cache_destroy().\n\nFurthermore, calling kfree(ub) immediately after synchronize_net() without\nclosing the socket first (or waiting after closing it) leaves a window\nwhere a concurrent receiver (tipc_udp_recv()) could start after\nsynchronize_net(), access ub, and suffer a UAF when kfree(ub) runs.\n\nTo fix this, we must defer dst_cache_destroy() and kfree(ub) until after\nwe have ensured that no more readers can see the bearer/socket and all\nexisting readers have finished:\n\n1. Defer rcast entry destruction (both dst_cache_destroy() and kfree())\n   to an RCU callback using call_rcu_hurry().\n   Using call_rcu_hurry() ensures the dst entries are released quickly.\n\n2. Release the bearer socket using udp_tunnel_sock_release() (stops\n   new receive readers).\n\n3. Call synchronize_net() to wait for all outstanding RCU readers\n   (both transmit and receive) to finish.\n\n4. Now that it is safe, call dst_cache_destroy() on the main bearer\n   cache, and free ub.\n\nNote: 3) and 4) can be changed later in net-next to also use\ncall_rcu_hurry() and get rid of the synchronize_net() latency."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"e9c1a793210f29f32ee4cf048e04d7d9bb3221cc","status":"affected","lessThan":"5a66ca574eee958123ee9d2822683964d42d656a","versionType":"git"},{"version":"e9c1a793210f29f32ee4cf048e04d7d9bb3221cc","status":"affected","lessThan":"6aeb4ba4fb098199e13723cfd04d9a749741f731","versionType":"git"},{"version":"e9c1a793210f29f32ee4cf048e04d7d9bb3221cc","status":"affected","lessThan":"6b0e29f7662c237e717f35dad746efe94715d0da","versionType":"git"},{"version":"e9c1a793210f29f32ee4cf048e04d7d9bb3221cc","status":"affected","lessThan":"3827ff67f9fbecd1086e33d23693ef6a1a9c6c38","versionType":"git"},{"version":"e9c1a793210f29f32ee4cf048e04d7d9bb3221cc","status":"affected","lessThan":"1c8393eefa3cadf4ca0b61119ad1321aa32d3c8c","versionType":"git"},{"version":"e9c1a793210f29f32ee4cf048e04d7d9bb3221cc","status":"affected","lessThan":"7116764ca53ff529335d7ab7c364a69f094b23a5","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/tipc/udp_media.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.3","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.3","versionType":"semver"},{"version":"6.1.191","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.160","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.114","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.57","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.5","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/tipc/udp_media.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/5a66ca574eee958123ee9d2822683964d42d656a"},{"url":"https://git.kernel.org/stable/c/6aeb4ba4fb098199e13723cfd04d9a749741f731"},{"url":"https://git.kernel.org/stable/c/6b0e29f7662c237e717f35dad746efe94715d0da"},{"url":"https://git.kernel.org/stable/c/3827ff67f9fbecd1086e33d23693ef6a1a9c6c38"},{"url":"https://git.kernel.org/stable/c/1c8393eefa3cadf4ca0b61119ad1321aa32d3c8c"},{"url":"https://git.kernel.org/stable/c/7116764ca53ff529335d7ab7c364a69f094b23a5"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":7.8,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:L - The UAF is in cleanup_bearer() during UDP bearer teardown, reached only via TIPC genetlink bearer disable (TIPC_NL_BEARER_DISABLE) or network-namespace exit; remote UDP/TIPC peers cannot initiate teardown, so exploitation requires local netlink/netns access even though concurrent xmit/recv may involve network I/O.\nAC:L - An attacker with namespace CAP_NET_ADMIN can script both teardown and concurrent traffic (enable/disable bearer or destroy netns while sending/receiving TIPC UDP on port 6118), controlling both sides of the RCU race; dst_cache_destroy()'s free_percpu() widens the window and syzbot triggered it reliably.\nPR:L - Bearer disable/enable and netns teardown require CAP_NET_ADMIN; TIPC genetlink ops use GENL_UNS_ADMIN_PERM and tipc_genl_family.netnsok=true, so unprivileged users obtain effective net-admin capability via user/network namespaces (unshare -Urn).\nUI:N - Exploitation needs no victim interaction beyond the attacker's own namespace/netlink operations and packet generation; no mount, file open, or other user-directed action is required.\nS:U - The use-after-free corrupts kernel heap memory within the same kernel security domain; impacts are kernel crash or local privilege escalation, not VM escape or cross-security-authority boundary crossing.\nC:H - Premature dst_cache_destroy() frees per-CPU cache memory while concurrent tipc_udp_xmit() may call dst_cache_get() on the freed object, and the post-synchronize_net() recv path dereferences freed udp_bearer, enabling kernel memory disclosure.\nI:H - UAF on dst_cache structures and udp_bearer allows heap shaping and control of freed-object contents, providing primitives for arbitrary kernel writes and potential control-flow hijacking/local privilege escalation.\nA:H - Concurrent use-after-free reliably causes kernel oops/panic (per commit: UAF on per-CPU cache pointer crashes) and can be triggered repeatedly during scripted bearer teardown loops."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-30T12:29:17.840Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.3","versionEndExcluding":"6.1.191"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.3","versionEndExcluding":"6.6.160"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.3","versionEndExcluding":"6.12.114"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.3","versionEndExcluding":"6.18.57"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.3","versionEndExcluding":"7.1.5"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.3","versionEndExcluding":"7.2"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-72404","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"total"}],"version":"2.0.3","timestamp":"2026-10-16T18:49:02.601623Z"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-16T18:55:21.804Z"}}]}}}