# Protego has exponential backtracking ReDoS in robots.txt URL wildcard matching

Advisory record · `GHSA-wjmf-p669-5m5p`

- **Identifiers:** `GHSA-wjmf-p669-5m5p` · `CVE-2026-55520` · `PYSEC-2026-3906`
- **State:** Confirmed
- **Severity:** CVSS 7.1 High
- **Critical:** No
- **Weakness (CWE):** [CWE-400](https://cwe.mitre.org/data/definitions/400.html) · [CWE-1333](https://cwe.mitre.org/data/definitions/1333.html)
- **Tags:** [Denial of service](https://agentprime.io/advisories/tag/dos.md)
- **Published:** 28 Aug 2026
- **Updated:** 10 Sept 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 28 Aug 2026, 18:43 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `protego` (PyPI): affected `<0.6.2`; fixed in `0.6.2`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> Protego, a Python robots.txt parser, is vulnerable before version 0.6.2 to a regular expression denial of service. A robots.txt file containing a specially crafted Allow or Disallow value with many asterisks can cause the matching call to hang for a time that grows with URL length. An attacker needs only to supply or control a robots.txt file that the parser processes. Upgrade to Protego 0.6.2 or later.

Written 1 Nov 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 7.1 High, CVSS 4.0: `CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0051, the 44th percentile, on 14 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 14:10 UTC: First seen by agentprime
- 31 Oct 2026, 14:10 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-wjmf-p669-5m5p)

## Sources

- [GitHub Advisory Database: GHSA-wjmf-p669-5m5p](https://github.com/advisories/GHSA-wjmf-p669-5m5p)
- [OSV: GHSA-wjmf-p669-5m5p](https://osv.dev/vulnerability/GHSA-wjmf-p669-5m5p)
- <https://github.com/scrapy/protego/security/advisories/GHSA-wjmf-p669-5m5p>
- <https://github.com/scrapy/protego/commit/785940181659bf440ba82f1da148fade5087e858>
- <https://github.com/scrapy/protego>
- <https://github.com/scrapy/protego/releases/tag/0.6.2>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-wjmf-p669-5m5p>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

---

The web page: <https://agentprime.io/advisories/GHSA-wjmf-p669-5m5p/>. Everything for agents: <https://agentprime.io/llms.txt>.