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CVE-2026-21876 β€” AI Deep Analysis Summary

CVSS 9.3 Β· Critical

Q1What is this vulnerability? (Essence + Consequences)

🚨 **Essence**: OWASP CRS WAF bypass due to Rule 922110 flaw. πŸ“‰ **Consequences**: Malicious character sets are ignored, allowing attacks to slip through the defense line.

Q2Root Cause? (CWE/Flaw)

πŸ›‘οΈ **CWE**: CWE-794 (Susceptibility to Malicious Character Sets). πŸ” **Flaw**: Defective handling of multipart requests in the rule engine.

Q3Who is affected? (Versions/Components)

πŸ‘₯ **Affected**: OWASP CRS Project. πŸ“¦ **Versions**: < 4.22.0 AND < 3.3.8. 🏷️ **Vendor**: coreruleset.

Q4What can hackers do? (Privileges/Data)

πŸ’» **Action**: Hackers bypass WAF detection. πŸ“‚ **Impact**: Potential data leakage or system compromise by injecting malicious characters that the WAF fails to flag.

Q5Is exploitation threshold high? (Auth/Config)

πŸ”“ **Threshold**: LOW. 🌐 **Config**: CVSS AV:N (Network), PR:N (No Privs), UI:N (No Interaction). Easy to exploit remotely.

Q6Is there a public Exp? (PoC/Wild Exploitation)

πŸ’₯ **Exploit**: YES. πŸ“‚ **PoC**: Public GitHub PoC available (docker container + minimal exploit). πŸš€ **Status**: Wild exploitation risk is high.

Q7How to self-check? (Features/Scanning)

πŸ” **Check**: Scan for OWASP CRS versions. πŸ“‹ **Feature**: Look for Rule 922110 in multipart request handling. πŸ› οΈ **Tool**: Use scanners to detect outdated CRS versions.

Q8Is it fixed officially? (Patch/Mitigation)

βœ… **Fixed**: YES. πŸ“₯ **Patch**: Upgrade to CRS v3.3.8+ or v4.22.0+. πŸ”— **Ref**: Official GitHub releases and commits.

Q9What if no patch? (Workaround)

🚧 **Workaround**: If unpatched, manually review Rule 922110 logic. πŸ›‘οΈ **Mitigation**: Implement strict input validation at the application layer. πŸ‘€ **Monitor**: Enhanced logging for multipart requests.

Q10Is it urgent? (Priority Suggestion)

πŸ”₯ **Urgency**: HIGH. 🚨 **Priority**: Immediate patching required. ⚠️ **Reason**: Critical WAF bypass with public PoC and low exploitation barrier.