{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2025-21673", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2024-12-29T08:45:45.736Z", "datePublished": "2025-01-31T11:25:35.922Z", "dateUpdated": "2026-08-05T11:53:31.173Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-05T11:53:31.173Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: fix double free of TCP_Server_Info::hostname\n\nWhen shutting down the server in cifs_put_tcp_session(), cifsd thread\nmight be reconnecting to multiple DFS targets before it realizes it\nshould exit the loop, so @server->hostname can't be freed as long as\ncifsd thread isn't done. Otherwise the following can happen:\n\n RIP: 0010:__slab_free+0x223/0x3c0\n Code: 5e 41 5f c3 cc cc cc cc 4c 89 de 4c 89 cf 44 89 44 24 08 4c 89\n 1c 24 e8 fb cf 8e 00 44 8b 44 24 08 4c 8b 1c 24 e9 5f fe ff ff <0f>\n 0b 41 f7 45 08 00 0d 21 00 0f 85 2d ff ff ff e9 1f ff ff ff 80\n RSP: 0018:ffffb26180dbfd08 EFLAGS: 00010246\n RAX: ffff8ea34728e510 RBX: ffff8ea34728e500 RCX: 0000000000800068\n RDX: 0000000000800068 RSI: 0000000000000000 RDI: ffff8ea340042400\n RBP: ffffe112041ca380 R08: 0000000000000001 R09: 0000000000000000\n R10: 6170732e31303000 R11: 70726f632e786563 R12: ffff8ea34728e500\n R13: ffff8ea340042400 R14: ffff8ea34728e500 R15: 0000000000800068\n FS: 0000000000000000(0000) GS:ffff8ea66fd80000(0000)\n 000000\n CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033\n CR2: 00007ffc25376080 CR3: 000000012a2ba001 CR4:\n PKRU: 55555554\n Call Trace:\n \n ? show_trace_log_lvl+0x1c4/0x2df\n ? show_trace_log_lvl+0x1c4/0x2df\n ? __reconnect_target_unlocked+0x3e/0x160 [cifs]\n ? __die_body.cold+0x8/0xd\n ? die+0x2b/0x50\n ? do_trap+0xce/0x120\n ? __slab_free+0x223/0x3c0\n ? do_error_trap+0x65/0x80\n ? __slab_free+0x223/0x3c0\n ? exc_invalid_op+0x4e/0x70\n ? __slab_free+0x223/0x3c0\n ? asm_exc_invalid_op+0x16/0x20\n ? __slab_free+0x223/0x3c0\n ? extract_hostname+0x5c/0xa0 [cifs]\n ? extract_hostname+0x5c/0xa0 [cifs]\n ? __kmalloc+0x4b/0x140\n __reconnect_target_unlocked+0x3e/0x160 [cifs]\n reconnect_dfs_server+0x145/0x430 [cifs]\n cifs_handle_standard+0x1ad/0x1d0 [cifs]\n cifs_demultiplex_thread+0x592/0x730 [cifs]\n ? __pfx_cifs_demultiplex_thread+0x10/0x10 [cifs]\n kthread+0xdd/0x100\n ? __pfx_kthread+0x10/0x10\n ret_from_fork+0x29/0x50\n " } ], "metrics": [ { "cvssV3_1": { "version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H", "baseScore": 9.8, "baseSeverity": "CRITICAL" }, "scenarios": [ { "lang": "en", "value": "AV:N - The bug lives in the SMB client's connection/reconnect handling, which processes data from the remote peer — the remote server controls when the TCP connection drops (forcing reconnect) and controls the DFS referral target list that drives the offending free loop. A compromised/malicious SMB-DFS file server, or an on-path attacker able to reset connections and inject referrals, reaches this over the network.\nAC:L - The attacker controls both sides of the race and the window size: it forces reconnects at will, supplies an arbitrarily long DFS target list, and can point targets at blackholed addresses so each `generic_ip_connect()` blocks for the TCP SYN-retry timeout (~130s) while `msleep(3000)` adds more, and the per-target loop never re-checks `tcpStatus`. The race can be retried unboundedly on every reconnect cycle, and it was hit in real-world operation.\nPR:N - The attacking SMB server holds no privileges on the victim client, and the vulnerable `__reconnect_target_unlocked()` path executes during socket reconnect, before SMB negotiate/session-setup — i.e. pre-authentication. The teardown side is likewise reachable via timer/workqueue-driven paths (`smb2_reconnect_server`, automount expiry) requiring no local privileges.\nUI:N - For an already-mounted DFS share (fstab/autofs, the normal enterprise deployment), reconnect, referral failover, and automount expiry are entirely server- and timer-driven, so no victim action occurs during the attack. The existing mount is a precondition of the deployment, not an in-attack user step.\nS:U - The double free corrupts the kernel slab allocator and impacts only kernel-managed resources within the same security authority. No VM, IOMMU, or sandbox boundary is crossed.\nC:H - A double free lets the same slab object be handed to two allocation sites, yielding type confusion and an arbitrary-read primitive. Additionally there is a direct leak: `reconn_set_ipaddr_from_hostname()` formats the freed string into a UNC and passes it to the `dns_query()` userspace upcall, exfiltrating reused kernel heap contents to userspace verbatim.\nI:H - Double free is a classic heap-corruption primitive — freelist manipulation via heap spraying gives a controlled write and enables control-flow hijacking and privilege escalation. The freed object is a small attacker-influenced `kmalloc` string in a heavily-used general-purpose cache, making reclaim straightforward.\nA:H - The reported effect is an immediate slab consistency BUG (`__slab_free` invalid-op) killing the cifsd kthread, and a panic under `panic_on_oops`. Even unexploited, the allocator corruption reliably destabilizes or crashes the whole system." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "fs/smb/client/connect.c" ], "versions": [ { "version": "7be3248f313930ff3d3436d4e9ddbe9fccc1f541", "lessThan": "1ea68070338518a1d31ce71e6abfe1b30001b27a", "status": "affected", "versionType": "git" }, { "version": "7be3248f313930ff3d3436d4e9ddbe9fccc1f541", "lessThan": "a2be5f2ba34d0c6d5ef2624b24e3d852561fcd6a", "status": "affected", "versionType": "git" }, { "version": "7be3248f313930ff3d3436d4e9ddbe9fccc1f541", "lessThan": "fa2f9906a7b333ba757a7dbae0713d8a5396186e", "status": "affected", "versionType": "git" }, { "version": "49f933bb3016269dc50074eac5f6033d127644f1", "status": "affected", "versionType": "git" }, { "version": "1c35a216ef77db708178ca225d796271f2f60a7a", "status": "affected", "versionType": "git" }, { "version": "5.14.19", "lessThan": "5.15", "status": "affected", "versionType": "semver" }, { "version": "5.15.3", "lessThan": "5.16", "status": "affected", "versionType": "semver" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "fs/smb/client/connect.c" ], "versions": [ { "version": "5.16", "status": "affected" }, { "version": "0", "lessThan": "5.16", "status": "unaffected", "versionType": "semver" }, { "version": "6.6.74", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.11", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.13", "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": "5.16", "versionEndExcluding": "6.6.74" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.16", "versionEndExcluding": "6.12.11" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.16", "versionEndExcluding": "6.13" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.14.19" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.15.3" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/1ea68070338518a1d31ce71e6abfe1b30001b27a" }, { "url": "https://git.kernel.org/stable/c/a2be5f2ba34d0c6d5ef2624b24e3d852561fcd6a" }, { "url": "https://git.kernel.org/stable/c/fa2f9906a7b333ba757a7dbae0713d8a5396186e" } ], "title": "smb: client: fix double free of TCP_Server_Info::hostname", "x_generator": { "engine": "bippy-1.2.0" } }, "adp": [ { "metrics": [ { "cvssV3_1": { "scope": "UNCHANGED", "version": "3.1", "baseScore": 5.5, "attackVector": "LOCAL", "baseSeverity": "MEDIUM", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H", "integrityImpact": "NONE", "userInteraction": "NONE", "attackComplexity": "LOW", "availabilityImpact": "HIGH", "privilegesRequired": "LOW", "confidentialityImpact": "NONE" } }, { "other": { "type": "ssvc", "content": { "id": "CVE-2025-21673", "role": "CISA Coordinator", "options": [ { "Exploitation": "none" }, { "Automatable": "no" }, { "Technical Impact": "partial" } ], "version": "2.0.3", "timestamp": "2025-10-01T19:52:08.291891Z" } } } ], "problemTypes": [ { "descriptions": [ { "lang": "en", "type": "CWE", "cweId": "CWE-415", "description": "CWE-415 Double Free" } ] } ], "title": "CISA ADP Vulnrichment", "providerMetadata": { "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2025-10-01T19:57:12.012Z" } } ] } }