{"id":"CVE-2026-89696","aliases":[],"url":"https://o3.security/vulnerability/CVE-2026-89696","summary":"nfsd: block non-SAVEFH ops after FOREIGN PUTFH to prevent NULL deref","details":"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.","published":"2026-09-11T19:46:15.030Z","modified":"2026-09-14T03:46:25.980688241Z","cvss":{"score":7.5,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"Linux","name":"Kernel","fixedVersion":"6.12.109"}],"fix":null,"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/311f7d926630940650447cbd1c932b076b40a6c4"},{"type":"WEB","url":"https://git.kernel.org/stable/c/35f248bd40b47b229d4999581df45b97daadd977"},{"type":"WEB","url":"https://git.kernel.org/stable/c/bf4d338dc8625d70c7f2cb0657d66851a7ac9154"},{"type":"WEB","url":"https://git.kernel.org/stable/c/c59738a00aa51b16adc1b5ceb7c80877168efb4d"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89696.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-89696"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-09-14T03:46:25.980688241Z"}}