{"id":"CVE-2025-21731","title":"In the Linux kernel, the following vulnerability has been resolved:\n\nnbd: don't allow reconnect after disconnect\n\nFollowing process can cause nbd_config UAF:\n\n1) grab nbd_config temporarily;\n\n2) nbd_genl_disconnect() flush all recv_work(…","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nnbd: don't allow reconnect after disconnect\n\nFollowing process can cause nbd_config UAF:\n\n1) grab nbd_config temporarily;\n\n2) nbd_genl_disconnect() flush all recv_work(…","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","cwe":["CWE-416"],"vendor":"linux","product":"linux_kernel","affected":["linux_kernel >= 4.12, < 5.4.291","linux_kernel >= 5.5, < 5.10.235","linux_kernel >= 5.11, < 5.15.179","linux_kernel >= 5.16, < 6.1.129","linux_kernel >= 6.2, < 6.6.76","linux_kernel >= 6.7, < 6.12.13","linux_kernel >= 6.13, < 6.13.2"],"patched":["linux_kernel 6.13.2"],"published":"2025-02-27","updated":"2026-07-14","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2025-21731","references":[{"url":"https://git.kernel.org/stable/c/6bef6222a3f6c7adb6396f77f25a3579d821b09a","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/844b8cdc681612ff24df62cdefddeab5772fadf1","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/9793bd5ae4bdbdb2dde401a3cab94a6bfd05e302","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/a8ee6ecde2b7bfb58c8a3afe8a9d2b848f580739","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/d208d2c52b652913b5eefc8ca434b0d6b757f68f","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/e3be8862d73cac833e0fb7602636c19c6cb94b11","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/e70a578487a47d7cf058904141e586684d1c3381","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/e7343fa33751cb07c1c56b666bf37cfca357130e","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://lists.debian.org/debian-lts-announce/2025/03/msg00028.html","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://cert-portal.siemens.com/productcert/html/ssa-019113.html","label":"0b142b55-0307-4c5a-b3c9-f314f3fb7c5e"}],"tags":["nvd","cve.org"],"epss":0.00231,"epssPercentile":0.1418,"ingestedAt":"2026-07-14T13:36:55.404Z","ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"total","timestamp":"2025-02-27T17:58:00.860096Z"},"slug":"CVE-2025-21731","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nnbd: don't allow reconnect after disconnect\n\nFollowing process can cause nbd_config UAF:\n\n1) grab nbd_config temporarily;\n\n2) nbd_genl_disconnect() flush all recv_work() and release the\ninitial reference:\n\n  nbd_genl_disconnect\n   nbd_disconnect_and_put\n    nbd_disconnect\n     flush_workqueue(nbd->recv_workq)\n    if (test_and_clear_bit(NBD_RT_HAS_CONFIG_REF, ...))\n     nbd_config_put\n     -> due to step 1), reference is still not zero\n\n3) nbd_genl_reconfigure() queue recv_work() again;\n\n  nbd_genl_reconfigure\n   config = nbd_get_config_unlocked(nbd)\n   if (!config)\n   -> succeed\n   if (!test_bit(NBD_RT_BOUND, ...))\n   -> succeed\n   nbd_reconnect_socket\n    queue_work(nbd->recv_workq, &args->work)\n\n4) step 1) release the reference;\n\n5) Finially, recv_work() will trigger UAF:\n\n  recv_work\n   nbd_config_put(nbd)\n   -> nbd_config is freed\n   atomic_dec(&config->recv_threads)\n   -> UAF\n\nFix the problem by clearing NBD_RT_BOUND in nbd_genl_disconnect(), so\nthat nbd_genl_reconfigure() will fail.\n\n## Affected\n\n- `linux_kernel >= 4.12, < 5.4.291`\n- `linux_kernel >= 5.5, < 5.10.235`\n- `linux_kernel >= 5.11, < 5.15.179`\n- `linux_kernel >= 5.16, < 6.1.129`\n- `linux_kernel >= 6.2, < 6.6.76`\n- `linux_kernel >= 6.7, < 6.12.13`\n- `linux_kernel >= 6.13, < 6.13.2`\n\n## Remediation\n\nUpgrade past the affected range:\n\n- `linux_kernel 6.13.2`","depth":"twilight","depthScore":43,"depthScoreParts":{"impact":42.9,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}