# CVE-2026-10645: Out-of-bounds read in Zephyr ext2 directory entry traversal from a crafted filesystem image

Status: published. Published: 2026-06-22. Updated: 2026-11-04.

The Zephyr ext2 filesystem driver (subsys/fs/ext2) trusted the on-disk directory entry fields de_rec_len and de_name_len when walking a directory block. ext2_fetch_direntry() guarded only with de_name_len > EXT2_MAX_FILE_NAME, but de_name_len is a uint8_t and EXT2_MAX_FILE_NAME is 255, so the check is always false; the function then memcpy'd up to 255 name bytes and the lookup/readdir paths advanced traversal by an unvalidated de_rec_len. Each directory block is read into a block_size-sized slab buffer, and block_off can be driven near the block end by preceding entries' rec_len, so the 8-byte header read and the subsequent name memcpy can read up to ~263 bytes past the end of the block buffer into adjacent heap/slab memory. On the readdir path those bytes are returned to the caller in fs_dirent.name, leaking adjacent kernel heap memory; a de_rec_len of 0 also causes a zero-progress infinite loop (denial of service), and the unlink path's memmove(de, next, next_reclen) over unvalidated records is an additional OOB read/write source. The defect is reached by any path-based operation (open, stat, unlink, rename, mkdir) or directory listing on a mounted ext2 volume, so a crafted or corrupted ext2 image on attacker-supplied storage (SD card, USB mass storage, or otherwise mounted image) triggers it. Affected: Zephyr ext2 from its introduction in v3.5.0 through v4.4.0. The fix validates rec_len and name_len in the parser and rejects entries whose header does not fit the remaining block or whose rec_len crosses the block boundary in every traversal caller.

## Remediation

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: zephyr) — https://github.com/zephyrproject-rtos/zephyr/commit/7cdb534a3c3daeaec18f656953857dcafa33a2bf
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: vulnerabilities@zephyrproject.org) — https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-hwrh-9h3x-vccm

## Affected products and versions

- zephyrproject / zephyr (zephyr): ≥ 3.5.0; < 4.6.0 (affected, semver). Source: CNA: zephyr

## NVD configuration conditions

Affected CPE matches depend on the following AND/OR and negation conditions:

```json
[
  {
    "negate": false,
    "nodes": [
      {
        "cpeMatch": [
          {
            "criteria": "cpe:2.3:o:zephyrproject:zephyr:*:*:*:*:*:*:*:*",
            "versionEndIncluding": "4.4.1",
            "vulnerable": true
          }
        ],
        "negate": false,
        "operator": "OR"
      }
    ],
    "operator": "OR"
  }
]
```

## Severity and prioritization

- CVSS 3.1: 4.9 (medium); CVSS:3.1/AV:P/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:H; source: CNA: zephyr

- CVSS 3.1: 5.5 (medium); CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H; source: NVD: nvd@nist.gov

- CVSS 3.1: 4.9 (medium); CVSS:3.1/AV:P/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:H; source: NVD: vulnerabilities@zephyrproject.org

- CISA KEV: No listing in collected sources

- EPSS: 0.16% as of 2026-11-03; percentile 4.96%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-125

## Exploit evidence

- exploit: https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-hwrh-9h3x-vccm (vulnerabilities@zephyrproject.org)

## References

- https://github.com/zephyrproject-rtos/zephyr/commit/7cdb534a3c3daeaec18f656953857dcafa33a2bf (CNA: zephyr; patch)

- https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-hwrh-9h3x-vccm (CNA: zephyr)

- https://github.com/zephyrproject-rtos/zephyr/commit/7cdb534a3c3daeaec18f656953857dcafa33a2bf (vulnerabilities@zephyrproject.org)

- https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-hwrh-9h3x-vccm (vulnerabilities@zephyrproject.org; Exploit, Patch, Vendor Advisory)

## Provenance

- CNA: zephyr: https://www.cve.org/CVERecord?id=CVE-2026-10645; retrieved 2026-11-04; source updated 2026-11-04

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-10645; retrieved 2026-11-04; source updated 2026-11-04

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-10645; retrieved 2026-11-04; source updated Not reported

Revision: 4046756499feaf662d33758a4d454b2de78ba7a439fe018f29f8cbe988cee2b9

Canonical: https://y2.dev/cve/CVE-2026-10645

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