CVE-2026-64298
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…
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.16%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
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.
- CVSS 3.1
- 7.1 HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H
- EPSS
- 0.16% probability · 6th percentile
- CISA KEV
- Not listed
- Affected
- linux/linux kernel
- Source
- 416baaa9-dc9f-4396-8d5f-8c081fb06d67
References
- https://git.kernel.org/stable/c/22c1fd1355ad4ca27aa7f0fa02719122dd92d9dePatch
- https://git.kernel.org/stable/c/30fdf4df6c3c00efec947e4ddf97f0fdd4473628Patch
- https://git.kernel.org/stable/c/4817c8974315b666e895b7d1bb83cd3664c323b1Patch
- https://git.kernel.org/stable/c/5140f099ecd8a2f2808b7f7b720ee1bad8468974Patch
- https://git.kernel.org/stable/c/6bd7d0a06b53c4e797e1a9cea0d2d41aa1b26230Patch
- https://git.kernel.org/stable/c/a937e92c1d00534b5c2e3e9f4381b7e988180797Patch
- https://git.kernel.org/stable/c/cb148a2762d644bff1894728e8835a9a4b84f9eaPatch
- https://git.kernel.org/stable/c/e36501b7d4abdcd6d69a7cb901b2f286b7a3d041Patch
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.