EUVD-2026-67865
GHSA-wjmf-p669-5m5p
Severity by source
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
Attacker serves robots.txt over the network (AV:N, AC:L, PR:N), but the crawling application must actively fetch it (UI:R); impact is availability-only with no scope change.
Primary rating from Vendor (https://github.com/scrapy/protego).
CVSS VectorVendor: https://github.com/scrapy/protego
Lifecycle Timeline
6Blast Radius
ecosystem impact- 673 pypi packages depend on protego (53 direct, 622 indirect)
Ecosystem-wide dependent count for version 0.6.2.
DescriptionCVE.org
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")
# freezesArticles & Coverage 1
AnalysisAI
Exponential backtracking ReDoS in Protego (pip/protego <= 0.6.1) allows any party who can serve a crafted robots.txt to freeze the can_fetch() call indefinitely, denying service to any application using this library for robots.txt compliance. A working proof-of-concept is publicly available in the GitHub security advisory GHSA-wjmf-p669-5m5p; the CVSS 4.0 score of 7.1 (VA:H) reflects meaningful availability risk for web-crawling deployments. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires three concurrent conditions: (1) the target application uses protego <= 0.6.1 to parse robots.txt; (2) the application fetches robots.txt from a domain the attacker controls or can influence (e.g., via DNS poisoning or by simply operating the target domain); and (3) the application subsequently calls `can_fetch()` with a URL that is a near-miss for the crafted wildcard pattern. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:N/UI:P/VA:H, score 7.1) accurately models the threat: a remote attacker with no credentials can cause complete availability loss in the vulnerable component, but only after the target application fetches the attacker-controlled robots.txt - captured by UI:P. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | Vendor-released patch: 0.6.2. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, identify all systems running Protego version 0.6.1 or earlier and obtain the patched version from PyPI. …
Sign in for detailed remediation steps and compensating controls.
Threat intelligence, references, and detailed analysis are available after sign-in.
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External POC / Exploit Code
Leaving vuln.today