Executive brief
Unfurl, a tool used for digital forensics and URL analysis, is vulnerable to a 'decompression bomb' attack. An attacker can send a specially crafted, highly compressed data packet that appears small but expands to gigabytes when processed by the server. This causes the system to run out of memory and crash, leading to a total service outage and preventing investigators from using the tool.
Technical details
A denial of service vulnerability exists in Unfurl's 'parse_compressed.py' component due to improper handling of highly compressed data (CWE-409). The application calls 'zlib.decompress()' on base64-encoded URL components without specifying a maximum output size (maxsize). A remote, unauthenticated attacker can exploit this by submitting a 'decompression bomb'—a small payload that expands exponentially—to the '/json/visjs' endpoint. This results in rapid memory exhaustion and service crashes. The issue is resolved in version 2026.04 by implementing 'safe_decompress' with strict size limits.
Affected products
- RyanDFIR / Obsidian Forensics Unfurl (dfir-unfurl) < 2026.04
Timeline
- 2026-01-28: advisory: Initial GitHub Security Advisory published
- 2026-04-05: patched: Version 2026.04 released with safe_decompress fix
- 2026-04-08: disclosed: NVD and VulnCheck public disclosure