Vulnerability Description
Flag Forge is a Capture The Flag (CTF) platform. Versions 2.3.2 and below have a Regular Expression Denial of Service (ReDoS) vulnerability in the user profile API endpoint (/api/user/[username]). The application constructs a regular expression dynamically using unescaped user input (the username parameter). An attacker can exploit this by sending a specially crafted username containing regex meta-characters (e.g., deeply nested groups or quantifiers), causing the MongoDB regex engine to consume excessive CPU resources. This can lead to Denial of Service for other users. The issue is fixed in version 2.3.3. To workaround this issue, implement a Web Application Firewall (WAF) rule to block requests containing regex meta-characters in the URL path.
CVSS Score
HIGH
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Flagforge | Flagforge | >= 2.0, < 2.3.3 |
Related Weaknesses (CWE)
References
FAQ
What is CVE-2026-21868?
CVE-2026-21868 is a vulnerability with a CVSS score of 7.5 (HIGH). Flag Forge is a Capture The Flag (CTF) platform. Versions 2.3.2 and below have a Regular Expression Denial of Service (ReDoS) vulnerability in the user profile API endpoint (/api/user/[username]). The...
How severe is CVE-2026-21868?
CVE-2026-21868 has been rated HIGH with a CVSS base score of 7.5/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-21868?
Check the references section above for vendor advisories and patch information. Affected products include: Flagforge Flagforge.