CVE-2020-25266

Vulnerability

In appimaged versions before 1.0.3, the daemon does not properly check whether a downloaded file is a valid AppImage. It relies only on scanning for ELF and AppImage type 2 headers, without verifying the full file structure. This allows a crafted MP3 file, which lacks a fixed file header and can embed ELF and AppImage headers at the start, to be accepted as an AppImage. The affected versions are all versions of appimaged and all libappimage versions older than 1.0.3 [1].

Exploitation

An attacker crafts an MP3 file that contains a valid AppImage payload (ELF header, executable, and SquashFS filesystem) at strategic positions so that the MP3 remains playable. The attacker places this file in a directory that appimaged monitors. appimaged scans all files regardless of extension, detects the ELF and AppImage headers, and proceeds to extract the desktop file from the SquashFS. The rogue desktop file can then override a system-installed application (e.g., Nautilus). No authentication or special privileges are required beyond the ability to place the file in a monitored directory [1].

Impact

A successful attack allows an attacker to install a malicious AppImage disguised as a non-executable media file. When the user launches the overridden application (e.g., Files/Nautilus), the attacker’s payload executes instead of the legitimate system binary. This leads to arbitrary code execution at the user’s privilege level, resulting in a full compromise of the user’s session and data [1].

Mitigation

The vulnerability is fixed in appimaged and libappimage version 1.0.3 [1]. Users should update to version 1.0.3 or later. No workaround is available; users can reduce risk by not placing untrusted files in directories monitored by appimaged. The CVE is not listed in CISA’s Known Exploited Vulnerabilities catalog.