# CVE-2026-31577: nilfs2: fix NULL i_assoc_inode dereference in nilfs_mdt_save_to_shadow_map

CVE-2026-31577 is fixed in linux on 1 platform, first by DEBIAN-CVE-2026-31577, released May 15, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-31577
- Priority: Routine
- CVSS: 5.5 (Moderate)
- EPSS: 0.0013
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Apr 24, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-31577

## Description

In the Linux kernel, the following vulnerability has been resolved:  nilfs2: fix NULL i_assoc_inode dereference in nilfs_mdt_save_to_shadow_map  The DAT inode's btree node cache (i_assoc_inode) is initialized lazily during btree operations. However, nilfs_mdt_save_to_shadow_map() assumes i_assoc_inode is already initialized when copying dirty pages to the shadow map during GC.  If NILFS_IOCTL_CLEAN_SEGMENTS is called immediately after mount before any btree operation has occurred on the DAT inode, i_assoc_inode is NULL leading to a general protection fault.  Fix this by calling nilfs_attach_btree_node_cache() on the DAT inode in nilfs_dat_read() at mount time, ensuring i_assoc_inode is always initialized before any GC operation can use it.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 6.1.176-1 | [DEBIAN-CVE-2026-31577](https://patchblox.com/security/data/fix/linux/debian-cve-2026-31577.md) | May 15, 2026 |
| Linux | linux Debian 13.5 (trixie) | 6.12.85-1 | [DEBIAN-CVE-2026-31577](https://patchblox.com/security/data/fix/linux/debian-cve-2026-31577.md) | May 15, 2026 |
| Linux | linux Debian 14 | 6.19.14-1 | [DEBIAN-CVE-2026-31577](https://patchblox.com/security/data/fix/linux/debian-cve-2026-31577.md) | May 15, 2026 |

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Data as of 2026-11-09T01:18:40Z 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 Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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