Vulnerability in Protego (CVE-2026-55520)
Summary
Vulnerability in Protego (CVE-2026-55520). Risk of unauthorized operations or information disclosure. Exploitable via robots.txt. Mitigation: upgrade to 0.6.2 or later.
Original description
The description as published by the source.
Problem description
Protego constructs regular expressions to match URLs against robots.txt Allow: and Disallow: directives, see protego._urlpattern._URLPattern._prepare_pattern_for_regex(). Every * in the directive value is translated into a lazy .*? regex piece, thus a specially crafted directive value with many asterisks may produce a regex that freezes the parser due to exponential backtracking.
Impact
Parsing a specially crafted robots.txt with protego.Protego.parse() and then trying to match an URL with protego.Protego.can_fetch() results in the latter call not returning for a period dependent on the length of the URL.
Proof of concept
from protego import Protego
robotstxt = f"""
User-agent: *
Disallow: /{"*1" * 12}*Z
"""
rp = Protego.parse(robotstxt)
url = "/" + "1" * 60
rp.can_fetch(url, "mybot") # freezes
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-55520 has been found in Protego.
Attackers can target a specific entry point like robots.txt over the network to misuse the product.
Risk of unauthorized operations or information disclosure.
What to do: upgrade Protego to 0.6.2 or later.
If unsure, ask your IT team or search "Protego CVE-2026-55520" on the vendor's site.
CVE-2026-55520 (Protego) — CWE-400
Attack surface: robots.txt
Patched: 0.6.2 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-400) exists in Protego. Attackers reach the vulnerable code path via robots.txt.
Check the vendor advisory for the affected versions of Protego. Attack surface: robots.txt.
Severity: ?. Risk of unauthorized operations or information disclosure.
Update to 0.6.2.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'Protego' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'Protego' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
Protegoを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade Protego to 0.6.2ステージング環境で 0.6.2 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Debian DEBIAN-CVE-2026-55520 python-protego
- Ubuntu UBUNTU-CVE-2026-55520 python-protego