{"id":"CVE-2026-64459","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-64459","generatedAt":"2026-10-28T07:03:53.647Z","title":"In the Linux kernel, the following vulnerability has been resolved: tcp: restore RCU grace period in tcp_ao_destroy_sock Commit 51e547e8c89c (\"tcp: Free TCP-AO/TCP-MD5 info/keys without RCU\") removed the call_rcu() callback from tcp_ao_destroy_sock(),…","description":"In the Linux kernel, the following vulnerability has been resolved:\n\ntcp: restore RCU grace period in tcp_ao_destroy_sock\n\nCommit 51e547e8c89c (\"tcp: Free TCP-AO/TCP-MD5 info/keys without RCU\")\nremoved the call_rcu() callback from tcp_ao_destroy_sock(), arguing that\n\"the destruction of info/keys is delayed until the socket destructor\"\nand therefore \"no one can discover it anymore\".\n\nThat argument does not hold for the call site in tcp_connect()\n(net/ipv4/tcp_output.c:4327-4332). At that point the socket is in\nTCP_SYN_SENT, has already been inserted into the inet ehash by\ninet_hash_connect() in tcp_v4_connect(), and is therefore very much\ndiscoverable: any softirq running tcp_v4_rcv() on another CPU can take\nthe socket out of the ehash, walk into tcp_inbound_hash(), and load\ntp->ao_info via implicit RCU before bh_lock_sock_nested() is taken on\nthe destroying CPU.\n\nThe reader path then enters __tcp_ao_do_lookup() (net/ipv4/tcp_ao.c:208)\nwhich re-loads tp->ao_info via rcu_dereference_check(); the re-load can\nstill observe the (about-to-be-freed) pointer because there is no\nsynchronize_rcu() between rcu_assign_pointer(tp->ao_info, NULL) and\ntcp_ao_info_free() in tcp_ao_destroy_sock(). The captured pointer is\nthen walked at line 223:\n\n\thlist_for_each_entry_rcu(key, &ao->head, node, ...)\n\nThe writer's synchronous kfree() is free to complete between the line\n218 re-fetch and the line 223 hlist iteration. The slab is reused\n(or simply LIST_POISON1-stamped if not yet reused) and the iteration\nwalks attacker-controlled or poison memory in softirq context.\n\nReproducer (no debug shim, stock x86_64 v7.1-rc2 SMP+KASAN, QEMU+KVM):\nan unprivileged uid=1000 process inside CLONE_NEWUSER|CLONE_NEWNET\ninstalls TCP_MD5SIG + TCP_AO_ADD_KEY on a TCP socket, sprays forged\nTCP-AO segments toward its eventual 4-tuple via raw sockets, then\ncalls connect(). The md5-wins reconciliation in tcp_connect() fires\ntcp_ao_destroy_sock(); the softirq backlog reader on the loopback\nNAPI path crashes on the freed ao->head.first walk:\n\n  Oops: general protection fault, probably for non-canonical\n    address 0xfbd59c000000002f\n  KASAN: maybe wild-memory-access in range\n    [0xdead000000000178-0xdead00000000017f]\n  CPU: 0 UID: 1000 PID: 100 Comm: repro_userns\n  RIP: 0010:__tcp_ao_do_lookup+0x107/0x1c0\n  Call Trace: <IRQ>\n    __tcp_ao_do_lookup+0x107/0x1c0\n    tcp_ao_inbound_lookup.constprop.0+0x12a/0x200\n    tcp_inbound_ao_hash+0x5ea/0x1520\n    tcp_inbound_hash+0x7ce/0x1240\n    tcp_v4_rcv+0x1e7a/0x3e10\n    ...\n\nRestore the RCU grace period: re-add struct rcu_head to tcp_ao_info\nand replace the synchronous tcp_ao_info_free() with a call_rcu()\ncallback. Readers that captured tp->ao_info before rcu_assign_pointer\nNULLed it now see the object remain valid until rcu_read_unlock().\nWith the patch applied the reproducer runs cleanly for 2000 iterations\non the same kernel build.","published":"2026-07-25T10:17:31.000Z","lastModified":"2026-08-17T05:17:51.000Z","status":"Received","sourceIdentifier":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","cvss":{"version":"3.1","score":9.8,"severity":"CRITICAL","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"},"cwe":[],"affected":[],"epss":{"score":0.00649,"percentile":0.50918,"date":"2026-10-27","history":[]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"high","text":"High impact if exploited, but EPSS currently rates exploitation as unlikely (0.65%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit."},"changes":[],"references":[{"url":"https://git.kernel.org/stable/c/4caf12c778fed3dc3824cf36263be5e2c491fbd0","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/657646c08c94ef7b9dbe468fe7828032216f9841","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/8bc4d43bccbd60efe85d0a44d5bf41762f2f0c30","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-64459","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}