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DEBIAN-CVE-2026-89696
No affected components available
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.
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The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a high impact on the availability of the system.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
Probability that this vulnerability will be exploited in the wild within the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
- CVE-2026-89696Upstream
- EUVD-2026-76608Upstream
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