# CVE-2026-64031

## Summary

- **CVE ID:** CVE-2026-64031
- **Severity:** HIGH
- **CVSS Score:** 7.8 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H)
- **CWE:** N/A
- **Published:** Jul 19, 2026
- **Last Modified:** Sep 14, 2026

## Description

In the Linux kernel, the following vulnerability has been resolved:

erofs: fix managed cache race for unaligned extents

After unaligned compressed extents were introduced, the following race
could occur:

[Thread 1]                                   [Thread 2]
(z_erofs_fill_bio_vec)
<handle a Z_EROFS_PREALLOCATED_FOLIO folio>
...
filemap_add_folio (1)
                                             (z_erofs_bind_cache)
                                             <the same folio is found..>
                                             ..
                                             ..
folio_attach_private (2)
                                             filemap_add_folio (3) again

Since (1) is executed but (2) hasn't been executed yet, it's possible
that another thread finds the same managed folio in z_erofs_bind_cache()
for a different pcluster and calls filemap_add_folio() again since
folio->private is still Z_EROFS_PREALLOCATED_FOLIO.

Fix this by explicitly clearing folio->private before making the folio
visible in the managed cache so that another pcluster can simply wait
on the locked managed folio as what we did for other shared cases [1].

This only impacts unaligned data compression (`-E48bit` with zstd,
for example).

[1] Commit 9e2f9d34dd12 ("erofs: handle overlapped pclusters out of
 crafted images properly") was originally introduced to handle crafted
 overlapped extents, but it addresses unaligned extents as well.

## Affected Products

- Linux — Linux (7361d1e3763baaf7b9349c576137851458ad38d1)
- Linux — Linux (6.15)
- Linux — Linux (0)
- Linux — Linux (6.18.34)
- Linux — Linux (7.0.11)
- Linux — Linux (7.1)
- Linux — Linux (722f0fcdb0bb7d12a5c6d9460b9a7de1f735f36d)

## References

- [CNA](https://git.kernel.org/stable/c/425d32d6288d7d845e486af9419bbedccd8c9103)
- [CNA](https://git.kernel.org/stable/c/038166f873c4caf6e85cfd4ea0c5a5ba297b4e8b)
- [CNA](https://git.kernel.org/stable/c/649932fc3815eda2f24eb4de4b3a5e94886ee0b9)
- [CNA](https://git.kernel.org/stable/c/2718cdb6db0fdbe375e61f2980aada27bafb323e)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.13%
- **EPSS Percentile:** 2.9

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-17._