# CVE-2026-31694

## Summary

Linux kernel FUSE readdir cache out-of-bounds write

## Description

A missing bounds check in the Linux kernel FUSE readdir cache allows a malicious FUSE server to overflow a page-cache page by 24 bytes. In `fs/fuse/readdir.c`, `fuse_add_dirent_to_cache()` computes the serialized directory-entry size from the server-controlled `namelen` field and copies it into a single page-cache page. The check `offset + reclen > PAGE_SIZE` only handles records that do not fit in the remaining space of the current page; it does not reject records larger than `PAGE_SIZE` itself. After the `FUSE_NAME_MAX` increase to `PATH_MAX-1` (4095) in Linux 6.16 (commit 27992ef80770d), a FUSE daemon can return a dirent with `namelen=4095`, producing a 4120-byte record that overflows a 4 KiB page by 24 bytes into the adjacent kernel page. This can be exploited for unprivileged local privilege escalation by corrupting the page-cache copy of `/etc/passwd`. Affected versions are reachable from v6.16 through v7.0-rc and stable branches before their respective fixes. Reproduction uses the public PoC at https://github.com/0xCyberstan/CVE-2026-31694-POC inside a QEMU/KVM VM running a vulnerable kernel.

## Metadata

- Product: Linux kernel (FUSE subsystem)
- Severity: high
- Status: open