{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2025-21955","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","state":"PUBLISHED","assignerShortName":"Linux","dateReserved":"2024-12-29T08:45:45.790Z","datePublished":"2025-04-01T15:46:55.724Z","dateUpdated":"2026-08-05T11:55:35.788Z"},"containers":{"cna":{"providerMetadata":{"orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux","dateUpdated":"2026-08-05T11:55:35.788Z"},"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: prevent connection release during oplock break notification\n\nksmbd_work could be freed when after connection release.\nIncrement r_count of ksmbd_conn to indicate that requests\nare not finished yet and to not release the connection."}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":8.8,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:N - ksmbd is the in-kernel SMB server listening on TCP/445; the entire path (oplock grant, oplock break trigger, and the connection reset that wins the race) is driven purely by SMB2 traffic from remote clients.\nAC:L - The attacker owns both sides of the race — connection A holds the oplock, connection B triggers the break notification, and the attacker chooses exactly when to reset A's socket — and can retry the sequence unlimited times over the network.\nPR:L - Reaching an oplock/lease break requires an established SMB2 session and tree connect (SMB2_CREATE with an oplock or lease context), so valid low-privileged share credentials (or a guest mapping) are needed; it is not a pre-authentication code path.\nUI:N - No victim action is required — the attacker's own two connections create the oplock, trigger the break, and tear down the connection entirely on their own schedule.\nS:U - The use-after-free is confined to kernel memory within the same security authority; no VM, IOMMU, or sandbox boundary is crossed.\nC:H - The freed ksmbd_conn/tcp_transport objects are dereferenced after release, and reclaiming those kmalloc-64 slots with attacker-sprayed data yields a read primitive over kernel memory and leaks server/session state.\nI:H - ksmbd_conn_write() performs an indirect call through conn->transport->ops->writev read out of the freed transport, giving control-flow hijack and arbitrary-write potential once the slab is reclaimed with controlled contents.\nA:H - Even without successful grooming the stale dereference of the freed connection, transport, and released socket reliably oopses or panics the kernel, killing the SMB server host."}]}],"affected":[{"product":"Linux","vendor":"Linux","defaultStatus":"unaffected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/smb/server/connection.c","fs/smb/server/connection.h","fs/smb/server/oplock.c","fs/smb/server/server.c"],"versions":[{"version":"0626e6641f6b467447c81dd7678a69c66f7746cf","lessThan":"09aeab68033161cb54f194da93e51a11aee6144b","status":"affected","versionType":"git"},{"version":"0626e6641f6b467447c81dd7678a69c66f7746cf","lessThan":"a4261bbc33fbf99b99c80aa3a2c5097611802980","status":"affected","versionType":"git"},{"version":"0626e6641f6b467447c81dd7678a69c66f7746cf","lessThan":"f17d1c63a76b0fe8e9c78023a86507a3a6d62cfa","status":"affected","versionType":"git"},{"version":"0626e6641f6b467447c81dd7678a69c66f7746cf","lessThan":"3aa660c059240e0c795217182cf7df32909dd917","status":"affected","versionType":"git"}]},{"product":"Linux","vendor":"Linux","defaultStatus":"affected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/smb/server/connection.c","fs/smb/server/connection.h","fs/smb/server/oplock.c","fs/smb/server/server.c"],"versions":[{"version":"5.15","status":"affected"},{"version":"0","lessThan":"5.15","status":"unaffected","versionType":"semver"},{"version":"6.6.84","lessThanOrEqual":"6.6.*","status":"unaffected","versionType":"semver"},{"version":"6.12.20","lessThanOrEqual":"6.12.*","status":"unaffected","versionType":"semver"},{"version":"6.13.8","lessThanOrEqual":"6.13.*","status":"unaffected","versionType":"semver"},{"version":"6.14","lessThanOrEqual":"*","status":"unaffected","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.15","versionEndExcluding":"6.6.84"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.15","versionEndExcluding":"6.12.20"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.15","versionEndExcluding":"6.13.8"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.15","versionEndExcluding":"6.14"}]}]}],"references":[{"url":"https://git.kernel.org/stable/c/09aeab68033161cb54f194da93e51a11aee6144b"},{"url":"https://git.kernel.org/stable/c/a4261bbc33fbf99b99c80aa3a2c5097611802980"},{"url":"https://git.kernel.org/stable/c/f17d1c63a76b0fe8e9c78023a86507a3a6d62cfa"},{"url":"https://git.kernel.org/stable/c/3aa660c059240e0c795217182cf7df32909dd917"}],"title":"ksmbd: prevent connection release during oplock break notification","x_generator":{"engine":"bippy-1.2.0"}}}}