# 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.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 8 Apr 2026
- **Updated:** 8 Oct 2026
- **Also known as:** GHSA-h5qv-qjv4-pc5m, PYSEC-2026-1294

## 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.

Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling), CWE-409 (Improper Handling of Highly Compressed Data (Data Amplification))

## Which versions are affected by CVE-2026-40036?

3 open source packages ship an affected version, including dfir-unfurl. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `dfir-unfurl` | PyPI | All versions | 20260405 |
| `dfir-unfurl` | PyPI | All versions | 20260405 |
| `dfir-unfurl` | PyPI | All versions | 20260405 |

Products: Ryandfir Unfurl.

## How do I fix CVE-2026-40036?

Upgrade dfir-unfurl to 20260405 or later.

## 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

- [CVE-2026-40035](https://insights.sbomify.com/CVE-2026-40035/): Unfurl - Werkzeug Debugger Exposure via String Config Parsing (critical 9.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-40036 and fix it if it is affected.

What it is: 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.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-40036 exists.

Affected packages and fixed versions:
- dfir-unfurl (PyPI): affected all versions; fixed in 20260405
- dfir-unfurl (PyPI): affected all versions; fixed in 20260405
- dfir-unfurl (PyPI): affected all versions; fixed in 20260405

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-40036/ (Markdown: https://insights.sbomify.com/CVE-2026-40036/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-40036
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-40036
- OSV: https://osv.dev/vulnerability/CVE-2026-40036

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-40036/
Summaries are generated and may contain mistakes; the official description above is the record.