Directory Entry Overflow in Linux Kernel FUSE Implementation

CVE-2026-31694

What is CVE-2026-31694?

CVE-2026-31694 is a vulnerability found in the Linux kernel's FUSE (Filesystem in Userspace) implementation. FUSE allows non-privileged users to create their own file systems without editing kernel code. This vulnerability arises from inadequate validation in the fuse_add_dirent_to_cache() function, where the serialized size of directory entries is not properly checked against the maximum allowable size. Specifically, a malicious FUSE server can send oversized directory entries, leading to a buffer overflow that compromises memory safety by allowing data to spill into adjacent kernel pages. This flaw could potentially lead to system instability, unauthorized access, and exploitation of additional vulnerabilities, emphasizing the importance of rapid mitigation strategies.

Potential impact of CVE-2026-31694

1. Memory Corruption: The overflow condition can corrupt kernel memory, leading to unpredictable behavior, crashes, or even system reboots, which can significantly disrupt operations for affected organizations.

2. Privilege Escalation: Attackers could exploit the buffer overflow to gain elevated privileges within the system. This could allow for executing arbitrary code or commands, which can compromise sensitive data or further infiltrate organizational resources.

3. Target for Malware Deployment: The vulnerability is exploitable by malicious FUSE servers, making systems using FUSE susceptible to targeted attacks, where ransomware or other forms of malware can be delivered and executed, thereby increasing the threat landscape against critical infrastructure.

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