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CVE-2026-89696

HIGHCVSS 7.5/10EPSS 0.67%

Last modified

CVE-2026-89696 is a high-severity vulnerability rated 7.5/10 on the CVSS scale. 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. EPSS estimates a 0.67% chance of exploitation in the next 30 days.

Description

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.

Metrics

CVSS 3.1
7.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS Probability
0.67%

50.0th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

VendorProductVersions
LinuxLinux>= b9e8638e3d9ed8334f1f7071e081860aac37e83e, < ffdc844e673d2bcb2af8c8c3eef8cdea59d0bf32; >= b9e8638e3d9ed8334f1f7071e081860aac37e83e, < 00c84f4eec715e501efc080a5670114189e42507; >= b9e8638e3d9ed8334f1f7071e081860aac37e83e, < 2d9846fd1c767920fddd4bde30eb35cd2969df13; >= b9e8638e3d9ed8334f1f7071e081860aac37e83e, < 977e6f006a7a3ffc4216ae6034f768f8de6fd138; >= b9e8638e3d9ed8334f1f7071e081860aac37e83e, < 35f248bd40b47b229d4999581df45b97daadd977; >= b9e8638e3d9ed8334f1f7071e081860aac37e83e, < 311f7d926630940650447cbd1c932b076b40a6c4; >= b9e8638e3d9ed8334f1f7071e081860aac37e83e, < bf4d338dc8625d70c7f2cb0657d66851a7ac9154; >= b9e8638e3d9ed8334f1f7071e081860aac37e83e, < c59738a00aa51b16adc1b5ceb7c80877168efb4d
LinuxLinux5.6

References

Timeline

Published
Last Modified
Status
Received

Frequently Asked Questions

What is CVE-2026-89696?
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.
How severe is CVE-2026-89696?
CVE-2026-89696 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 0.67% probability of exploitation in the next 30 days.
How do I fix CVE-2026-89696?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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Source: NVD / NIST