{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-64401", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-07-19T15:36:31.785Z", "datePublished": "2026-07-25T08:50:44.361Z", "dateUpdated": "2026-08-17T04:54:59.017Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-17T04:54:59.017Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: resolve SWN tcon from live registrations\n\ncifs_swn_notify() looks up a witness registration by id under\ncifs_swnreg_idr_mutex, drops the mutex, and then uses the registration's\ncached tcon pointer. That pointer is not a lifetime reference, and it is\nnot a stable representative once cifs_get_swn_reg() lets multiple tcons\nfor the same net/share name share one registration id.\n\nA same-share second mount can keep the cifs_swn_reg alive after the first\ntcon unregisters and is freed. The registration then still points at the\nfreed first tcon, so taking tc_lock or incrementing tc_count through\nswnreg->tcon only moves the use-after-free earlier. Taking tc_lock while\nholding cifs_swnreg_idr_mutex also violates the documented CIFS lock\norder.\n\nFix this by making the registration store only the stable witness\nidentity: id, net name, share name, and notify flags. When a notify\narrives, copy that identity under cifs_swnreg_idr_mutex, drop the mutex,\nthen find and pin a live witness tcon that currently matches the net/share\npair under the normal cifs_tcp_ses_lock -> tc_lock order. The notification\npath uses that pinned tcon directly and drops the reference when done.\n\nRegistration and unregister messages now use the live tcon passed by the\ncaller instead of a cached tcon in the registration. The final unregister\nsend is folded into cifs_swn_unregister() while the registration is still\nprotected by cifs_swnreg_idr_mutex. This removes the previous\nfind/drop/reacquire raw-pointer window. The release path only removes the\nidr entry and frees the stable identity strings.\n\nThis preserves the intended one-registration/many-tcon behavior: a\nregistration id represents a net/share pair, and notify handling acts on a\nlive representative selected at use time. It also preserves CLIENT_MOVE\nordering for the representative tcon because the old-IP unregister is sent\nbefore cifs_swn_register() sends the new-IP register." } ], "metrics": [ { "cvssV3_1": { "version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "baseScore": 7.8, "baseSeverity": "HIGH" }, "scenarios": [ { "lang": "en", "value": "AV:L - The UAF is locally reachable through the world-readable /proc/fs/cifs/DebugData path and, on earlier affected kernels, unrestricted SWN generic-netlink notifications.\nAC:L - A same-share second mount deterministically preserves the registration after the first tcon is freed; repeated proc reads or notifications then dereference the stale pointer without requiring an uncontrollable race.\nPR:L - An unprivileged local user can read /proc/fs/cifs/DebugData, and affected kernels predating the companion netlink authorization fix also allowed unprivileged SWN_NOTIFY messages. User namespaces do not grant CIFS mount authority, but no mount privilege is needed once normal mount turnover creates the stale registration.\nUI:N - Once a witness-enabled registration exists, exploitation requires no further victim action; the attacker can invoke the local trigger directly.\nS:U - Successful exploitation compromises the host kernel within the same security authority and does not inherently cross a VM, IOMMU, or other scope boundary.\nC:H - The heap UAF involves attacker-reclaimable cifs_tcon and cifs_swn_reg objects whose pointer chains reach session credentials and arbitrary kernel memory, enabling high-impact disclosure primitives.\nI:H - Reclaiming the freed objects can redirect client-move and reconnect operations through attacker-influenced pointers, providing arbitrary-write and control-flow-hijacking potential.\nA:H - Dereferencing the freed tcon or registration can cause an immediate kernel oops or panic, and the periodic echo worker can repeatedly exercise the stale pointer." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "fs/smb/client/cifs_swn.c", "fs/smb/client/trace.h" ], "versions": [ { "version": "fed979a7e082bd9f25f9002c3c4f8740dacd0bc8", "lessThan": "51d18db392e5386a7bb9e816d611f14e600cca3c", "status": "affected", "versionType": "git" }, { "version": "fed979a7e082bd9f25f9002c3c4f8740dacd0bc8", "lessThan": "aa3c0cab4b28c5007ec570c63e1d6ad6943ed0fd", "status": "affected", "versionType": "git" }, { "version": "fed979a7e082bd9f25f9002c3c4f8740dacd0bc8", "lessThan": "945b4a4a54497db1dcb2f20ef801a84e884dac21", "status": "affected", "versionType": "git" }, { "version": "fed979a7e082bd9f25f9002c3c4f8740dacd0bc8", "lessThan": "91b8a58c6ac15c7db6518f696389933282f88da7", "status": "affected", "versionType": "git" }, { "version": "fed979a7e082bd9f25f9002c3c4f8740dacd0bc8", "lessThan": "0700f946659d0ab2352ec8a9b1c6fc74b13a27d7", "status": "affected", "versionType": "git" }, { "version": "fed979a7e082bd9f25f9002c3c4f8740dacd0bc8", "lessThan": "ec457f9afe5ae9538bdcd58fd4cb442b9787e183", "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/client/cifs_swn.c", "fs/smb/client/trace.h" ], "versions": [ { "version": "5.11", "status": "affected" }, { "version": "0", "lessThan": "5.11", "status": "unaffected", "versionType": "semver" }, { "version": "6.1.178", "lessThanOrEqual": "6.1.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.6.145", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.97", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.18.39", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.1.4", "lessThanOrEqual": "7.1.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.2", "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": "5.11", "versionEndExcluding": "6.1.178" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.11", "versionEndExcluding": "6.6.145" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.11", "versionEndExcluding": "6.12.97" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.11", "versionEndExcluding": "6.18.39" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.11", "versionEndExcluding": "7.1.4" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.11", "versionEndExcluding": "7.2" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/51d18db392e5386a7bb9e816d611f14e600cca3c" }, { "url": "https://git.kernel.org/stable/c/aa3c0cab4b28c5007ec570c63e1d6ad6943ed0fd" }, { "url": "https://git.kernel.org/stable/c/945b4a4a54497db1dcb2f20ef801a84e884dac21" }, { "url": "https://git.kernel.org/stable/c/91b8a58c6ac15c7db6518f696389933282f88da7" }, { "url": "https://git.kernel.org/stable/c/0700f946659d0ab2352ec8a9b1c6fc74b13a27d7" }, { "url": "https://git.kernel.org/stable/c/ec457f9afe5ae9538bdcd58fd4cb442b9787e183" } ], "title": "smb: client: resolve SWN tcon from live registrations", "x_generator": { "engine": "bippy-1.2.0" } } } }