CVE-2026-40036 Unfurl < 2026.04 - Denial of Service via Unbounded zlib Decompression
Remote attackers can cause denial of service by submitting highly compressed payloads that exhaust server memory in the Unfurl library.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-40036?
CVE-2026-40036 is a high-severity denial of service vulnerability in obsidianforensics unfurl, published on 8 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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.
Which versions are affected by CVE-2026-40036?
3 open source packages ship an affected version, including dfir-unfurl. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
dfir-unfurl PyPI | All versions | 20260405 |
dfir-unfurl PyPI | All versions | 20260405 |
dfir-unfurl PyPI | All versions | 20260405 |
Products include Ryandfir Unfurl.
How do I fix CVE-2026-40036?
Upgrade dfir-unfurl to 20260405 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-40036 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-40036 exists.
Other vulnerabilities in obsidianforensics unfurl
Sources
Also known as GHSA-h5qv-qjv4-pc5m, PYSEC-2026-1294.