CVE-2026-90234
HighCVSS 7.5Exploitation Probability (EPSS)
Low risk40th percentile - higher than 40% of all known CVEs
Summary
In the Linux kernel's NFS subsystem, when the client fails to record a delegation received from the server, it does not send DELEGRETURN. This causes the server to believe the client still holds the delegation, leading to issues with delegation recall and loops in the client's state manager. The fix returns the delegation in these error paths.
Risk Assessment
Failure to send DELEGRETURN can lead to infinite loops in the client's state manager and performance issues. It may also cause incorrect behavior during delegation recall.
Recommendation
Apply the Linux kernel patch that sends DELEGRETURN in the error paths of nfs_inode_set_delegation() when a delegation cannot be recorded.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: NFS: Return a delegation the client fails to record When an NFS server grants a delegation in an OPEN reply, nfs_inode_set_delegation() records it on the client. However, three of its error flows return without sending DELEGRETURN. A delegation can be relinquished only by DELEGRETURN (RFC 8881 Section 20.2.4), so dropping one silently leaves the server believing the client still holds it. If the server happens to recall that delegation, the client answers CB_RECALL with NFS4ERR_BADHANDLE because it has no record of the stateid. The server revokes the delegation and moves it onto its cl_revoked list, because the client never sends the FREE_STATEID that would drain it. Every subsequent SEQUENCE reply then carries SEQ4_STATUS_RECALLABLE_STATE_REVOKED, and the client's state manager loops issuing TEST_STATEID across its delegations without ever clearing the condition. The window is easy to reach now that a server offers a write delegation on any write OPEN: a delegation recalled for one opener races a re-open that the server answers with a fresh write delegation. Instead of dropping it, hand the delegation back during these error flows.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS