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CVE-2026-21876 — Proof-of-concept exploit for CVE-2026-21876 demonstrating multipart charset bypass of OWASP CRS WAF in Flask, ASP.NET, and Spring Boot applications. | Kitploit
Tools/GitHubGitHub/daytriftnewgen/cve-2026-21876
Vulnerability AnalysisIDS/IPS EvasionWeb Application ExploitationWAF BypassWeb SecurityPenetration Testing
GitHubdaytriftnewgen/cve-2026-21876

CVE-2026-21876

Proof-of-concept exploit for CVE-2026-21876 demonstrating multipart charset bypass of OWASP CRS WAF in Flask, ASP.NET, and Spring Boot applications.

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123 months agoNot yet reviewed

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CVE-2026-21876 (OWASP CRS WAF bypass)

CVE-2026-21876 docker container + minimal PoC.

I would like to thank @airween and @fzipi separately for their quick response! The vulnerability fix was ready in a very short time.

PoC

Run:

cd springboot_undertow_stand # or aspnet_stand
docker compose up --build
python3 demo/send.py            # BASELINE -> 403, BYPASS -> 200 + reconstructed payload

References

  • Github security advisory
  • OWASP CRS walkthrough blogpost
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