Answer in brief
CVE-2026-89696 records a Unknown severity vulnerability in nfsd: block non-SAVEFH ops after FOREIGN PUTFH to prevent NULL deref. The current sources do not mark it as known exploited. The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| Linux/Linuxgeneric | >=b9e8638e3d9ed8334f1f7071e081860aac37e83e <35f248bd40b47b229d4999581df45b97daadd977 || >=b9e8638e3d9ed8334f1f7071e081860aac37e83e <311f7d926630940650447cbd1c932b076b40a6c4 || >=b9e8638e3d9ed8334f1f7071e081860aac37e83e <bf4d338dc8625d70c7f2cb0657d66851a7ac9154 || >=b9e8638e3d9ed8334f1f7071e081860aac37e83e <c59738a00aa51b16adc1b5ceb7c80877168efb4d | 35f248bd40b47b229d4999581df45b97daadd977, 311f7d926630940650447cbd1c932b076b40a6c4, bf4d338dc8625d70c7f2cb0657d66851a7ac9154, c59738a00aa51b16adc1b5ceb7c80877168efb4d |
| Linux/Linuxgeneric | 5.6 | Not reported |
Published upstream
Sep 11, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Sep 11, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Sep 11, 2026
In the Linux kernel, the following vulnerability has been resolved: nfsd: block non-SAVEFH ops after FOREIGN PUTFH to prevent NULL deref When CONFIG_NFSD_V4_2_INTER_SSC is enabled, nfsd4_putfh() can return success with fh_dentry and fh_export both NULL if fh_verify() returns nfserr_stale and putfh->no_verify is true. The NFSD4_FH_FOREIGN flag is set, but the compound dispatch loop only uses this flag to bypass the nfserr_nofilehandle check -- it does not prevent subsequent ops from running with a NULL fh_dentry. A remote client can exploit this by crafting a COMPOUND that includes an inter-SSC COPY (which causes check_if_stalefh_allowed() to set no_verify=true on the saved PUTFH) with an additional op inserted between the source PUTFH and SAVEFH. For example, SETATTR calls fh_want_write() which dereferences fh_export->ex_path.mnt without calling fh_verify() first, causing a NULL pointer dereference in the nfsd kthread. Fix this by gating the dispatch loop: when NFSD4_FH_FOREIGN is set and fh_dentry is NULL, only OP_SAVEFH (needed for the inter-SSC flow) and ops with ALLOWED_WITHOUT_FH (which don't need a resolved filehandle) may proceed. All other ops receive nfserr_stale, per RFC 7862 Section 15.2.3 which specifies that foreign filehandle validation is deferred to the consuming operation and NFS4ERR_STALE returned at that point.
Quoted source text, attributed separately from HOL analysis.