Vulnerability · Published Apr 8, 2026 · Assigned by VulnCheck

CVE-2026-40036Unfurl < 2026.04 - Denial of Service via Unbounded zlib Decompression

High 7.5

In plain English

A high-severity resource allocation without limits in unfurl from obsidianforensics. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 44% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.5High

Exploit odds (30 days)0.5%top 55.8% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official description

Unfurl before 2026.04 contains an unbounded zlib decompression vulnerability in parse_compressed.py that allows remote attackers to cause denial of service. Attackers can submit highly compressed payloads via URL parameters to the /json/visjs endpoint that expand to gigabytes, exhausting server memory and crashing the service.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
PyPI	dfir-unfurl	20260405	GHSA-h5qv-qjv4-pc5m
PyPI	dfir-unfurl	20260405	PYSEC-2026-1294

Affected products (as reported)

Vendor	Product	Versions
obsidianforensics	unfurl	0 – before 2026.04

Weakness: CWE-770, CWE-409 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

GHSA Advisory GHSA-h5qv-qjv4-pc5m vendor-advisory
VulnCheck Advisory: dfir-unfurl - Denial of Service via Unbounded zlib Decompression release-notes, patch
https://www.vulncheck.com/advisories/dfir-unfurl-denial-of-service-via-unbounded-zlib-decompression third-party-advisory