GHSA-MJ8V-3X8M-9RX7
Vulnerability from github – Published: 2026-07-25 12:31 – Updated: 2026-07-27 06:30In 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.
{
"affected": [],
"aliases": [
"CVE-2026-64298"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-07-25T10:17:10Z",
"severity": "HIGH"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nNFSv4: include MAY_WRITE in open permission mask for O_TRUNC\n\nPOSIX requires write permission to truncate a file, so an open() that\nspecifies O_TRUNC must be authorized for write access regardless of the\nO_ACCMODE access mode.\n\nnfs_open_permission_mask() builds the access mask passed to\nnfs_may_open(), which is the local authorization gate for OPENs the\nclient serves itself from a cached write delegation via the\ncan_open_delegated() path in nfs4_try_open_cached(). The mask is\nderived from O_ACCMODE alone, so an open(O_RDONLY | O_TRUNC) against a\nfile the caller cannot write requests only MAY_READ and passes the\nlocal check. The OPEN is then satisfied locally and the truncation is\nissued to the server as a SETATTR(size=0) over the delegation stateid,\nwhich the server accepts under standard write-delegation semantics.\nPOSIX requires that this open fail with EACCES.\n\nInclude MAY_WRITE in the mask whenever O_TRUNC is set so the local\ncheck matches the access the server would have enforced.",
"id": "GHSA-mj8v-3x8m-9rx7",
"modified": "2026-07-27T06:30:31Z",
"published": "2026-07-25T12:31:30Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-64298"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/22c1fd1355ad4ca27aa7f0fa02719122dd92d9de"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/30fdf4df6c3c00efec947e4ddf97f0fdd4473628"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/4817c8974315b666e895b7d1bb83cd3664c323b1"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/5140f099ecd8a2f2808b7f7b720ee1bad8468974"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/6bd7d0a06b53c4e797e1a9cea0d2d41aa1b26230"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/a937e92c1d00534b5c2e3e9f4381b7e988180797"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/cb148a2762d644bff1894728e8835a9a4b84f9ea"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/e36501b7d4abdcd6d69a7cb901b2f286b7a3d041"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H",
"type": "CVSS_V3"
}
]
}
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