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CVE-2026-64298VulnerabilityPublished 07/25/2026

In the Linux kernel, the following vulnerability has been resolved: NFSv4: include MAY_WRITE in open permission mask for O_TRUNC POSIX requires… (CVE-2026-64298)

Source GCVE Database

Severity
Medium

No CVSS score published yet

Exploitation

Not in CISA KEV, no exploitation reported

EPSS
0.1% chance of exploitation in 30 days – higher than 3% of CVEs

What to do

AI-suggested

A fix has been implemented in the Linux kernel to include write permission in the open permission mask when O_TRUNC is used. Users should apply the official kernel updates that contain this fix. Since this is a kernel-level issue, updating to a patched kernel version is the recommended remediation. Patch status is not explicitly confirmed here; users should consult the Linux kernel vendor advisory for the specific fixed versions and update accordingly.

Description

In the Linux kernel, the following vulnerability has been resolved: NFSv4: include MAY_WRITE in open permission mask for O_TRUNC POSIX requires write permission to truncate a file, so an open() that specifies O_TRUNC must be authorized for write access regardless of the O_ACCMODE access mode. nfs_open_permission_mask() builds the access mask passed to nfs_may_open(), which is the local authorization gate for OPENs the client serves itself from a cached write delegation via the can_open_delegated() path in nfs4_try_open_cached(). The mask is derived from O_ACCMODE alone, so an open(O_RDONLY | O_TRUNC) against a file the caller cannot write requests only MAY_READ and passes the local check. The OPEN is then satisfied locally and the truncation is issued to the server as a SETATTR(size=0) over the delegation stateid, which the server accepts under standard write-delegation semantics. POSIX requires that this open fail with EACCES. Include MAY_WRITE in the mask whenever O_TRUNC is set so the local check matches the access the server would have enforced.

References