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 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.
CSIRTS triage
- What
- This vulnerability includes MAY_WRITE in the open permission mask for NFSv4 O_TRUNC.
- Who is affected
- Deployments using the NFSv4 protocol.
- Urgency
- Remediation is necessary to ensure correct permission handling.
- Action
- Apply the fix for CVE-2026-64298.
AI-assisted analysis generated from the source advisory — verify against the original.
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Exploitation outlook
- Low exploitation risk0.16% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 6% of all EPSS-scored CVEs.
Advisory coverage (2)
External references
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