{"id":"CVE-2025-39977","title":"futex: Prevent use-after-free during requeue-PI","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nfutex: Prevent use-after-free during requeue-PI\n\nsyzbot managed to trigger the following race:\n\n   T1                               T2\n\n futex_wait_requeue_pi()\n   fute…","severity":"high","cvss":7.8,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","cvssSource":"cna","vendor":"Linux","product":"Linux","affected":["Linux >= 07d91ef510fb16a2e0ca7453222105835b7ba3b8 < cb5d19a61274b51b49601214a87af573b43d60fa","Linux >= 07d91ef510fb16a2e0ca7453222105835b7ba3b8 < 348736955ed6ca6e99ca24b93b1d3fbfe352c181","Linux >= 07d91ef510fb16a2e0ca7453222105835b7ba3b8 < a170b9c0dde83312b8b58ccc91509c7c15711641","Linux >= 07d91ef510fb16a2e0ca7453222105835b7ba3b8 < d824b2dbdcfe3c390278dd9652ea526168ef6850","Linux >= 07d91ef510fb16a2e0ca7453222105835b7ba3b8 < b549113738e8c751b613118032a724b772aa83f2","Linux 5.15"],"published":"2025-10-15","updated":"2026-09-08","sourceUpdated":"2026-09-08T08:42:39.132Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2025-39977","references":[{"url":"https://git.kernel.org/stable/c/cb5d19a61274b51b49601214a87af573b43d60fa"},{"url":"https://git.kernel.org/stable/c/348736955ed6ca6e99ca24b93b1d3fbfe352c181"},{"url":"https://git.kernel.org/stable/c/a170b9c0dde83312b8b58ccc91509c7c15711641"},{"url":"https://git.kernel.org/stable/c/d824b2dbdcfe3c390278dd9652ea526168ef6850"},{"url":"https://git.kernel.org/stable/c/b549113738e8c751b613118032a724b772aa83f2"}],"tags":["cve.org"],"epss":0.0015,"epssPercentile":0.04573,"ingestedAt":"2026-09-08T15:33:26.996Z","slug":"CVE-2025-39977","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nfutex: Prevent use-after-free during requeue-PI\n\nsyzbot managed to trigger the following race:\n\n   T1                               T2\n\n futex_wait_requeue_pi()\n   futex_do_wait()\n     schedule()\n                               futex_requeue()\n                                 futex_proxy_trylock_atomic()\n                                   futex_requeue_pi_prepare()\n                                   requeue_pi_wake_futex()\n                                     futex_requeue_pi_complete()\n                                      /* preempt */\n\n         * timeout/ signal wakes T1 *\n\n   futex_requeue_pi_wakeup_sync() // Q_REQUEUE_PI_LOCKED\n   futex_hash_put()\n  // back to userland, on stack futex_q is garbage\n\n                                      /* back */\n                                     wake_up_state(q->task, TASK_NORMAL);\n\nIn this scenario futex_wait_requeue_pi() is able to leave without using\nfutex_q::lock_ptr for synchronization.\n\nThis can be prevented by reading futex_q::task before updating the\nfutex_q::requeue_state. A reference on the task_struct is not needed\nbecause requeue_pi_wake_futex() is invoked with a spinlock_t held which\nimplies a RCU read section.\n\nEven if T1 terminates immediately after, the task_struct will remain valid\nduring T2's wake_up_state().  A READ_ONCE on futex_q::task before\nfutex_requeue_pi_complete() is enough because it ensures that the variable\nis read before the state is updated.\n\nRead futex_q::task before updating the requeue state, use it for the\nfollowing wakeup.\n\n## Affected\n\n- `Linux >= 07d91ef510fb16a2e0ca7453222105835b7ba3b8 < cb5d19a61274b51b49601214a87af573b43d60fa`\n- `Linux >= 07d91ef510fb16a2e0ca7453222105835b7ba3b8 < 348736955ed6ca6e99ca24b93b1d3fbfe352c181`\n- `Linux >= 07d91ef510fb16a2e0ca7453222105835b7ba3b8 < a170b9c0dde83312b8b58ccc91509c7c15711641`\n- `Linux >= 07d91ef510fb16a2e0ca7453222105835b7ba3b8 < d824b2dbdcfe3c390278dd9652ea526168ef6850`\n- `Linux >= 07d91ef510fb16a2e0ca7453222105835b7ba3b8 < b549113738e8c751b613118032a724b772aa83f2`\n- `Linux 5.15`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":43,"depthScoreParts":{"impact":42.9,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}