Attack Chain

1. Crafted Archive Creation: An attacker creates a malicious archive file (e.g., .tar, .zip) containing specially crafted entries that leverage path traversal sequences (e.g., ../), hardlinks targeting sensitive files, symlinks pointing outside the target directory, or files with setuid/setgid bits.
2. Delivery: The malicious archive is delivered to a victim system. This could occur via various methods, such as embedding it in a software supply chain update, a malicious email attachment, or a download from a compromised website.
3. Initiation of Extraction: An application or script using the vulnerable decompress or @xhmikosr/decompress library attempts to extract the delivered archive to a specified output directory.
4. Path Traversal/File Write: Due to the flawed path containment check, the library incorrectly resolves paths for entries like output/../sibling-dir/malicious_file, allowing the attacker to write files to arbitrary locations outside the intended extraction directory.
5. Hardlink/Symlink Abuse: The library creates hardlink entries pointing to sensitive files (e.g., /etc/shadow) or symlink entries that redirect subsequent writes or reads to arbitrary locations on the filesystem, exposing or modifying sensitive data.
6. Privilege Escalation: If the extraction process runs with elevated privileges (e.g., as root), the attacker-crafted archive creates a file with setuid/setgid bits preserved, leading to a privileged executable that the attacker can then invoke for system-wide compromise.
7. Impact: The attacker achieves arbitrary file write/read, information disclosure (e.g., sensitive configuration files, credentials), or privilege escalation on the affected system, enabling further malicious activities.

Impact

The vulnerability allows for severe consequences, including arbitrary file writes, arbitrary file reads, and privilege escalation. If an attacker can deliver a specially crafted archive, they can overwrite critical system files, modify configuration, extract sensitive data like credentials, or create setuid/setgid executables. This is particularly concerning in environments where archive extraction is performed with elevated privileges, such as CI/CD pipelines, container build processes, or automated software installation scripts, leading to full system compromise. Any application that processes untrusted archives using the affected libraries is at risk.

Recommendation

• Patch CVE-2026-53486 immediately: Upgrade @xhmikosr/decompress to version 10.2.1 or 11.1.3 or later.
• Migrate from decompress: For applications using the unmaintained decompress package, migrate to @xhmikosr/decompress 11.1.3 or later, as decompress will not receive a fix for CVE-2026-53486.
• Implement least privilege: Ensure archive extraction processes are run with the lowest possible privileges to mitigate the impact of CVE-2026-53486, specifically preventing the creation of setuid/setgid files.
• Validate archive contents: Implement post-extraction validation to check for and reject any symlinks or hardlinks pointing outside the target directory or any files with unexpected mode bits, as a temporary workaround for CVE-2026-53486 if immediate patching is not possible.