{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-89696", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-09-11T19:38:34.750Z", "datePublished": "2026-09-11T19:46:15.030Z", "dateUpdated": "2026-10-19T08:51:09.479Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-10-19T08:51:09.479Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: block non-SAVEFH ops after FOREIGN PUTFH to prevent NULL deref\n\nWhen CONFIG_NFSD_V4_2_INTER_SSC is enabled, nfsd4_putfh() can return\nsuccess with fh_dentry and fh_export both NULL if fh_verify() returns\nnfserr_stale and putfh->no_verify is true. The NFSD4_FH_FOREIGN flag\nis set, but the compound dispatch loop only uses this flag to bypass\nthe nfserr_nofilehandle check -- it does not prevent subsequent ops\nfrom running with a NULL fh_dentry.\n\nA remote client can exploit this by crafting a COMPOUND that includes\nan inter-SSC COPY (which causes check_if_stalefh_allowed() to set\nno_verify=true on the saved PUTFH) with an additional op inserted\nbetween the source PUTFH and SAVEFH. For example, SETATTR calls\nfh_want_write() which dereferences fh_export->ex_path.mnt without\ncalling fh_verify() first, causing a NULL pointer dereference in the\nnfsd kthread.\n\nFix this by gating the dispatch loop: when NFSD4_FH_FOREIGN is set\nand fh_dentry is NULL, only OP_SAVEFH (needed for the inter-SSC flow)\nand ops with ALLOWED_WITHOUT_FH (which don't need a resolved\nfilehandle) may proceed. All other ops receive nfserr_stale, per\nRFC 7862 Section 15.2.3 which specifies that foreign filehandle\nvalidation is deferred to the consuming operation and NFS4ERR_STALE\nreturned at that point." } ], "metrics": [ { "cvssV3_1": { "version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H", "baseScore": 7.5, "baseSeverity": "HIGH" }, "scenarios": [ { "lang": "en", "value": "AV:N - The bug is in nfsd NFSv4 COMPOUND dispatch and is triggered by a crafted NFSv4.2 COMPOUND over TCP/2049 (PUTFH of a stale fh, then SETATTR, with an inter-SSC COPY in the same compound). No local access is required.\nAC:L - After EXCHANGE_ID/CREATE_SESSION, the attacker fully controls the compound that marks the source PUTFH no_verify and inserts SETATTR before SAVEFH, so fh_want_write hits NULL fh_export deterministically with no race or layout dependency.\nPR:N - AUTH_SYS (the usual nfsd configuration) verifies no secret; a client just asserts a UID to create a session. SETATTR then runs on the FOREIGN fh without fh_verify, so no export access check or other credential gate is reached.\nUI:N - The attacker sends the COMPOUND directly to nfsd; no administrator or victim user action is required at exploitation time.\nS:U - The NULL dereference oopses the nfsd kthread in the host kernel's own authority and does not cross a VM, IOMMU, or sandbox boundary.\nC:N - After the stale FOREIGN PUTFH, fh_export and fh_dentry are NULL rather than dangling or attacker-controlled, so the fault is on the first load of fh_export->ex_path.mnt with no disclosure.\nI:N - This is a pure NULL pointer dereference in fh_want_write with no write to attacker-influenced memory and no control-flow hijack primitive.\nA:H - The NULL dereference oopses the nfsd kthread and can be replayed to exhaust nfsd threads, denying NFS service; with panic_on_oops it panics the host." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "fs/nfsd/nfs4proc.c" ], "versions": [ { "version": "b9e8638e3d9ed8334f1f7071e081860aac37e83e", "lessThan": "ffdc844e673d2bcb2af8c8c3eef8cdea59d0bf32", "status": "affected", "versionType": "git" }, { "version": "b9e8638e3d9ed8334f1f7071e081860aac37e83e", "lessThan": "00c84f4eec715e501efc080a5670114189e42507", "status": "affected", "versionType": "git" }, { "version": "b9e8638e3d9ed8334f1f7071e081860aac37e83e", "lessThan": "2d9846fd1c767920fddd4bde30eb35cd2969df13", "status": "affected", "versionType": "git" }, { "version": "b9e8638e3d9ed8334f1f7071e081860aac37e83e", "lessThan": "977e6f006a7a3ffc4216ae6034f768f8de6fd138", "status": "affected", "versionType": "git" }, { "version": "b9e8638e3d9ed8334f1f7071e081860aac37e83e", "lessThan": "35f248bd40b47b229d4999581df45b97daadd977", "status": "affected", "versionType": "git" }, { "version": "b9e8638e3d9ed8334f1f7071e081860aac37e83e", "lessThan": "311f7d926630940650447cbd1c932b076b40a6c4", "status": "affected", "versionType": "git" }, { "version": "b9e8638e3d9ed8334f1f7071e081860aac37e83e", "lessThan": "bf4d338dc8625d70c7f2cb0657d66851a7ac9154", "status": "affected", "versionType": "git" }, { "version": "b9e8638e3d9ed8334f1f7071e081860aac37e83e", "lessThan": "c59738a00aa51b16adc1b5ceb7c80877168efb4d", "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/nfsd/nfs4proc.c" ], "versions": [ { "version": "5.6", "status": "affected" }, { "version": "0", "lessThan": "5.6", "status": "unaffected", "versionType": "semver" }, { "version": "5.10.270", "lessThanOrEqual": "5.10.*", "status": "unaffected", "versionType": "semver" }, { "version": "5.15.221", "lessThanOrEqual": "5.15.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.1.188", "lessThanOrEqual": "6.1.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.6.157", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.109", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.18.50", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.2.4", "lessThanOrEqual": "7.2.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.3", "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": "5.6", "versionEndExcluding": "5.10.270" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.6", "versionEndExcluding": "5.15.221" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.6", "versionEndExcluding": "6.1.188" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.6", "versionEndExcluding": "6.6.157" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.6", "versionEndExcluding": "6.12.109" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.6", "versionEndExcluding": "6.18.50" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.6", "versionEndExcluding": "7.2.4" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.6", "versionEndExcluding": "7.3" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/ffdc844e673d2bcb2af8c8c3eef8cdea59d0bf32" }, { "url": "https://git.kernel.org/stable/c/00c84f4eec715e501efc080a5670114189e42507" }, { "url": "https://git.kernel.org/stable/c/2d9846fd1c767920fddd4bde30eb35cd2969df13" }, { "url": "https://git.kernel.org/stable/c/977e6f006a7a3ffc4216ae6034f768f8de6fd138" }, { "url": "https://git.kernel.org/stable/c/35f248bd40b47b229d4999581df45b97daadd977" }, { "url": "https://git.kernel.org/stable/c/311f7d926630940650447cbd1c932b076b40a6c4" }, { "url": "https://git.kernel.org/stable/c/bf4d338dc8625d70c7f2cb0657d66851a7ac9154" }, { "url": "https://git.kernel.org/stable/c/c59738a00aa51b16adc1b5ceb7c80877168efb4d" } ], "title": "nfsd: block non-SAVEFH ops after FOREIGN PUTFH to prevent NULL deref", "x_generator": { "engine": "bippy-1.2.0" } } } }