{"id":"CVE-2026-64109","title":"af_unix: Fix UAF read of tail->len in unix_stream_data_wait()","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\naf_unix: Fix UAF read of tail->len in unix_stream_data_wait()\n\nunix_stream_data_wait() does skb_peek_tail(&sk->sk_receive_queue) without\nholding any lock that prevents …","severity":"high","cvss":8.8,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H","cvssSource":"cna","vendor":"Linux","product":"Linux","affected":["Linux >= 2b514574f7e88c8498027ee366fd6e7aae5aa4b5 < 26342087fac93b3932e6af61dc91ec029cb8a623","Linux >= 2b514574f7e88c8498027ee366fd6e7aae5aa4b5 < 38bccb927d83d7d52e5b20015a172a0b6101d11e","Linux >= 2b514574f7e88c8498027ee366fd6e7aae5aa4b5 < acdff9907478e82208475b1151700d0b71dcdc63","Linux >= 2b514574f7e88c8498027ee366fd6e7aae5aa4b5 < 5f162f95a95834f06a8ec6140889272ad12e842f","Linux >= 2b514574f7e88c8498027ee366fd6e7aae5aa4b5 < be309f8eae8b474a4a617eaae01324da996fc719","Linux 4.2"],"ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"total","timestamp":"2026-10-16T15:36:24.265690Z"},"published":"2026-07-19","updated":"2026-10-16","sourceUpdated":"2026-10-16T15:42:22.490Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-64109","references":[{"url":"https://git.kernel.org/stable/c/26342087fac93b3932e6af61dc91ec029cb8a623"},{"url":"https://git.kernel.org/stable/c/38bccb927d83d7d52e5b20015a172a0b6101d11e"},{"url":"https://git.kernel.org/stable/c/acdff9907478e82208475b1151700d0b71dcdc63"},{"url":"https://git.kernel.org/stable/c/5f162f95a95834f06a8ec6140889272ad12e842f"},{"url":"https://git.kernel.org/stable/c/be309f8eae8b474a4a617eaae01324da996fc719"}],"tags":["cve.org"],"epss":0.00129,"epssPercentile":0.02221,"ingestedAt":"2026-10-16T17:24:46.804Z","slug":"CVE-2026-64109","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\naf_unix: Fix UAF read of tail->len in unix_stream_data_wait()\n\nunix_stream_data_wait() does skb_peek_tail(&sk->sk_receive_queue) without\nholding any lock that prevents SKBs on that queue from being dequeued and\nfreed.\nThis has been the case since commit 79f632c71bea (\"unix/stream: fix\npeeking with an offset larger than data in queue\").\nThe first consequence of this is that the pointer comparison\n`tail != last` can be false even if `last` semantically refers to an\nalready-freed SKB while `tail` is a new SKB allocated at the same address;\nwhich can cause unix_stream_data_wait() to wrongly keep blocking after new\ndata has arrived, but only in a weird scenario where a peeking recv() and\na normal recv() on the same socket are racing, which is probably not a\nreal problem.\n\nBut since commit 2b514574f7e8 (\"net: af_unix: implement splice for stream\naf_unix sockets\"), `tail` is actually dereferenced, which can cause UAF in\nthe following race scenario (where test_setup() runs single-threaded,\nand afterwards, test_thread1() and test_thread2() run concurrently in\ntwo threads:\n```\nstatic int socks[2];\nvoid test_setup(void) {\n  socketpair(AF_UNIX, SOCK_STREAM, 0, socks);\n  send(socks[1], \"A\", 1, 0);\n  int peekoff = 1;\n  setsockopt(socks[0], SOL_SOCKET, SO_PEEK_OFF, &peekoff, sizeof(peekoff));\n}\nvoid test_thread1(void) {\n  char dummy;\n  recv(socks[0], &dummy, 1, MSG_PEEK);\n}\nvoid test_thread2(void) {\n  char dummy;\n  recv(socks[0], &dummy, 1, 0);\n  shutdown(socks[1], SHUT_WR);\n}\n```\n\nwhen racing like this:\n```\nthread1                       thread2\nunix_stream_read_generic\n  mutex_lock(&u->iolock)\n  skb_peek(&sk->sk_receive_queue)\n  skb_peek_next(skb, &sk->sk_receive_queue)\n  mutex_unlock(&u->iolock)\n                              unix_stream_read_generic\n                                unix_state_lock(sk)\n                                skb_peek(&sk->sk_receive_queue)\n                                unix_state_unlock(sk)\n  unix_stream_data_wait\n    unix_state_lock(sk)\n    tail = skb_peek_tail(&sk->sk_receive_queue)\n                                spin_lock(&sk->sk_receive_queue.lock)\n                                __skb_unlink(skb, &sk->sk_receive_queue)\n                                spin_unlock(&sk->sk_receive_queue.lock)\n                                consume_skb(skb) [frees the SKB]\n    `tail != last`: false\n    `tail`: true\n    `tail->len != last_len` ***UAF***\n```\n\nFix the UAF by removing the read of tail->len; checking tail->len would\nonly make sense if SKBs in the receive queue of a UNIX socket could grow,\nwhich can no longer happen.\n\nKuniyuki explained:\n\n> When commit 869e7c62486e (\"net: af_unix: implement stream sendpage\n> support\") added sendpage() support, data could be appended to the last\n> skb in the receiver's queue.\n>\n> That's why we needed to check if the length of the last skb was changed\n> while waiting for new data in unix_stream_data_wait().\n>\n> However, commit a0dbf5f818f9 (\"af_unix: Support MSG_SPLICE_PAGES\") and\n> commit 57d44a354a43 (\"unix: Convert unix_stream_sendpage() to use\n> MSG_SPLICE_PAGES\") refactored sendmsg(), and now data is always added\n> to a new skb.\n\nThat means this fix is not suitable for kernels before 6.5.\n\n## Affected\n\n- `Linux >= 2b514574f7e88c8498027ee366fd6e7aae5aa4b5 < 26342087fac93b3932e6af61dc91ec029cb8a623`\n- `Linux >= 2b514574f7e88c8498027ee366fd6e7aae5aa4b5 < 38bccb927d83d7d52e5b20015a172a0b6101d11e`\n- `Linux >= 2b514574f7e88c8498027ee366fd6e7aae5aa4b5 < acdff9907478e82208475b1151700d0b71dcdc63`\n- `Linux >= 2b514574f7e88c8498027ee366fd6e7aae5aa4b5 < 5f162f95a95834f06a8ec6140889272ad12e842f`\n- `Linux >= 2b514574f7e88c8498027ee366fd6e7aae5aa4b5 < be309f8eae8b474a4a617eaae01324da996fc719`\n- `Linux 4.2`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":48,"depthScoreParts":{"impact":48.4,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}