# CVE-2026-89839: f2fs: use the mount idmap for the owner check in f2fs_xattr_advise_set()

CVE-2026-89839 is fixed in 2 products on 1 platform, first by DEBIAN-CVE-2026-89839, released September 23, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-89839
- Priority: High
- CVSS: 7.1 (Moderate)
- EPSS: 0.0020
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Sep 16, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-89839

## Description

In the Linux kernel, the following vulnerability has been resolved:  f2fs: use the mount idmap for the owner check in f2fs_xattr_advise_set()  f2fs_xattr_advise_set() calls inode_owner_or_capable() with &nop_mnt_idmap before allowing the "system.advise" xattr to be set, instead of the idmap that the VFS passes to the ->set() handler.  f2fs supports idmapped mounts, so on such a mount this checks the caller's fsuid against the unmapped on-disk owner rather than the mapped owner: the actual owner can be wrongly denied with -EPERM and an unrelated caller wrongly allowed.  Pass the handler's idmap instead.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.12.111-1 | [DEBIAN-CVE-2026-89839](https://patchblox.com/security/data/fix/linux/debian-cve-2026-89839.md) | Sep 23, 2026 |
| Linux | linux Debian 14 | 7.2.6-1 | [DEBIAN-CVE-2026-89839](https://patchblox.com/security/data/fix/linux/debian-cve-2026-89839.md) | Sep 23, 2026 |
| Linux | linux-6.12 Debian 12.15 (bookworm) | 6.12.111-1~deb12u1 | [DEBIAN-CVE-2026-89839](https://patchblox.com/security/data/fix/linux/debian-cve-2026-89839.md) | Sep 23, 2026 |

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Data as of 2026-11-09T13:31:49Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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