Individual skill
testing-for-regex-dos-redos
Testing web applications for Regular Expression Denial of Service (ReDoS), where crafted input forces a backtracking regex engine into super-linear (polynomial or exponential) processing time, hanging worker threads and causing denial of service. Also covers blind regex injection for char-by-char secret exfiltration when the attacker controls the pattern. Activates when input is matched against complex validators or when stored regex rules are attacker-influenced.
internal/tools/skills/data/web-application-security/testing-for-regex-dos-redos/SKILL.md
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- Last checked
- Nov 7, 2026
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- 1,310
- Repository last updated
- Nov 7, 2026
- License
- Apache-2.0
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- cybersecurity Repository topic
- security Repository topic
- bug-bounty Repository topic
- automation Repository topic
- autonomous-pentesting Repository topic
- ai-agent Repository topic
- ai-security Repository topic
- ethical-hacking Repository topic
- golang Repository topic
- penetration-testing Repository topic
- penetration-testing Declared skill tag
- redos Declared skill tag
- denial-of-service Declared skill tag
- owasp Declared skill tag
- web-security Declared skill tag
- security Derived category
- testing Derived category
- security-application Derived category
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# Testing for Regex Denial of Service (ReDoS)
## When to Use
- During authorized assessments of endpoints that validate input with regexes (email, URL, username, phone, "sanitizers")
- When the application reflects processing time or has visible per-request latency you can measure
- When stored rules, search patterns, or filters let an attacker supply or influence the regex itself (blind regex injection)
- When reviewing source/config and you can read the actual patterns in use
- When testing JS (browser/Node `RegExp`), Python `re`, Java `java.util.regex`, or PCRE — all backtracking engines
## Prerequisites
- **Authorization**: ReDoS is a DoS technique; confirm the scope explicitly allows latency/availability testing, ideally against staging
- **Measurement tooling**: `curl -w`, Burp Suite timing, or a small script that doubles input length and records latency