CVE-2026-55520

7.1 HIGH 0.5% exploit odds Fix listed Denial of service Library

What it is

Protego is a pure-Python robots.txt parser with support for modern conventions. Prior to 0.6.2, protego._urlpattern._URLPattern._prepare_pattern_for_regex translates every asterisk in an Allow or Disallow directive into a lazy regular-expression wildcard, so a directive containing many asterisks creates exponential backtracking. After protego.Protego.parse processes a crafted robots.txt file, protego.Protego.can_fetch can spend an attacker-controlled period matching a near-miss URL and deny service to the crawler. The vulnerable path is src/protego/_urlpattern.py in the _URLPattern match logic. This issue is fixed in version 0.6.2.

At a glance

Exploitability: Can be exploited over the network without logging in, but needs a user to act. High risk of service disruption.
Exploit odds: 0.5% chance of exploitation in the next 30 days (EPSS).
Fix: A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

2026-08-28 20:18 UTC PublishedDisclosed publicly on CVE.org and NVD
2026-09-09 21:09 UTC Last updatedMost recent change to the record

Why it ranks here

Exploited in the wild: no, CISA does not list it.
Exploit odds: 0.5% in the next 30 days (EPSS).
Severity: 7.1 HIGH (CVSS).
Fix: a patch or advisory is linked.

Details

Published: 2026-08-28 20:18 UTC
Last modified: 2026-09-09 21:09 UTC
Exploit probability: 0.5% · EPSS, next 30 days
Weakness: CWE-400 · Uncontrolled resource consumption
Record status: Deferred

Attack profile CVSS 4.0 · 7.1

Attack vector: Network
Complexity: Low
Attack requirements: None
Privileges needed: None
User interaction: Passive
Confidentiality: None
Integrity: None
Availability: High

Raw vector

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2026-55520.md and follow it. Check whether this project is affected by CVE-2026-55520. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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Fix and advisories

References

NVD record · CVE.org record