{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-72404", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-08-09T03:40:39.925Z", "datePublished": "2026-08-15T05:56:28.124Z", "dateUpdated": "2026-08-17T05:43:44.084Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-17T05:43:44.084Z" }, "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." } ], "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." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "net/tipc/udp_media.c" ], "versions": [ { "version": "e9c1a793210f29f32ee4cf048e04d7d9bb3221cc", "lessThan": "1c8393eefa3cadf4ca0b61119ad1321aa32d3c8c", "status": "affected", "versionType": "git" }, { "version": "e9c1a793210f29f32ee4cf048e04d7d9bb3221cc", "lessThan": "7116764ca53ff529335d7ab7c364a69f094b23a5", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "net/tipc/udp_media.c" ], "versions": [ { "version": "5.3", "status": "affected" }, { "version": "0", "lessThan": "5.3", "status": "unaffected", "versionType": "semver" }, { "version": "7.1.5", "lessThanOrEqual": "7.1.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.2", "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": "5.3", "versionEndExcluding": "7.1.5" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.3", "versionEndExcluding": "7.2" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/1c8393eefa3cadf4ca0b61119ad1321aa32d3c8c" }, { "url": "https://git.kernel.org/stable/c/7116764ca53ff529335d7ab7c364a69f094b23a5" } ], "title": "tipc: fix UAF in cleanup_bearer() due to premature dst_cache_destroy()", "x_generator": { "engine": "bippy-1.2.0" } } } }