{"id":"CVE-2025-21731","state":"PUBLISHED","title":"nbd: don't allow reconnect after disconnect","description":"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() 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.","publishedAt":"2025-02-27T02:07:35.927Z","updatedAt":"2026-10-15T01:03:51.467Z","severity":{"score":7.8,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","source":"CISA-ADP"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"b7aa3d39385dc2d95899f9e379623fef446a2acd","status":"affected","lessThan":"e70a578487a47d7cf058904141e586684d1c3381","versionType":"git"},{"version":"b7aa3d39385dc2d95899f9e379623fef446a2acd","status":"affected","lessThan":"6bef6222a3f6c7adb6396f77f25a3579d821b09a","versionType":"git"},{"version":"b7aa3d39385dc2d95899f9e379623fef446a2acd","status":"affected","lessThan":"e3be8862d73cac833e0fb7602636c19c6cb94b11","versionType":"git"},{"version":"b7aa3d39385dc2d95899f9e379623fef446a2acd","status":"affected","lessThan":"e7343fa33751cb07c1c56b666bf37cfca357130e","versionType":"git"},{"version":"b7aa3d39385dc2d95899f9e379623fef446a2acd","status":"affected","lessThan":"d208d2c52b652913b5eefc8ca434b0d6b757f68f","versionType":"git"},{"version":"b7aa3d39385dc2d95899f9e379623fef446a2acd","status":"affected","lessThan":"a8ee6ecde2b7bfb58c8a3afe8a9d2b848f580739","versionType":"git"},{"version":"b7aa3d39385dc2d95899f9e379623fef446a2acd","status":"affected","lessThan":"9793bd5ae4bdbdb2dde401a3cab94a6bfd05e302","versionType":"git"},{"version":"b7aa3d39385dc2d95899f9e379623fef446a2acd","status":"affected","lessThan":"844b8cdc681612ff24df62cdefddeab5772fadf1","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/block/nbd.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"4.12","status":"affected"},{"version":"0","status":"unaffected","lessThan":"4.12","versionType":"semver"},{"version":"5.4.291","status":"unaffected","lessThanOrEqual":"5.4.*","versionType":"semver"},{"version":"5.10.235","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.179","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.129","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.76","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.13","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.13.2","status":"unaffected","lessThanOrEqual":"6.13.*","versionType":"semver"},{"version":"6.14","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/block/nbd.c"]}],"references":["https://git.kernel.org/stable/c/e70a578487a47d7cf058904141e586684d1c3381","https://git.kernel.org/stable/c/6bef6222a3f6c7adb6396f77f25a3579d821b09a","https://git.kernel.org/stable/c/e3be8862d73cac833e0fb7602636c19c6cb94b11","https://git.kernel.org/stable/c/e7343fa33751cb07c1c56b666bf37cfca357130e","https://git.kernel.org/stable/c/d208d2c52b652913b5eefc8ca434b0d6b757f68f","https://git.kernel.org/stable/c/a8ee6ecde2b7bfb58c8a3afe8a9d2b848f580739","https://git.kernel.org/stable/c/9793bd5ae4bdbdb2dde401a3cab94a6bfd05e302","https://git.kernel.org/stable/c/844b8cdc681612ff24df62cdefddeab5772fadf1","https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html","https://lists.debian.org/debian-lts-announce/2025/03/msg00028.html","https://cert-portal.siemens.com/productcert/html/ssa-019113.html","https://cert-portal.siemens.com/productcert/html/ssa-457936.html","https://cert-portal.siemens.com/productcert/html/ssa-784472.html"],"weaknesses":["CWE-416"],"ingestedAt":"2026-10-29T20:08:39.238Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2025/21xxx/CVE-2025-21731.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2025-21731","state":"PUBLISHED","datePublished":"2025-02-27T02:07:35.927Z","dateUpdated":"2026-10-15T01:03:51.467Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2024-12-29T08:45:45.755Z"},"containers":{"cna":{"title":"nbd: don't allow reconnect after disconnect","descriptions":[{"lang":"en","value":"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() 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 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