Protego has exponential backtracking ReDoS in robots.txt URL wildcard matching
Published Aug 28, 2026 · Updated Nov 3, 2026
Original summary
Normalized public record · Updated Nov 3, 2026
Protego has exponential backtracking ReDoS in robots.txt URL wildcard matching
Publisher and source text is retained separately from QFinch interpretation.
QFinch assessment
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.
Potential impact
Parsing a specially crafted robots.txt with protego.Protego.parse() and then trying to match an URL with protego.Protego.canfetch() results in the latter call not returning for a period dependent on the length of the URL.
Evidence: public source recordsAffected products
| Affected package, product or range | Fix status |
|---|---|
| Consult the referenced vendor advisory for affected versions. | Consult source advisory |
Matching a version is only one part of assessing exposure. QFinch has not assessed your environment on this public page.
Remediation
Apply the vendor-supported fixed release or mitigation, then verify the affected component is no longer reachable.
- Confirm the affected product and reachable code path exist in your environment.
- Apply the vendor-supported patch or mitigation from the primary advisory.
- Rescan the exact deployed revision and retain verification evidence.
Evidence coverage
- SSVC priority
- LOW
- Confidence
- Not available
- Aliases
- None reported
Scores appear only when corresponding evidence exists. Missing data is never interpreted as zero risk.
Sources and record history
Record history
Published Aug 28, 2026 · Last refreshed Nov 3, 2026