CVE-2026-21868
HIGHCVSS Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
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2Description
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.
Analysis
Flagforge versions 2.3.2 and earlier suffer from a Regular Expression Denial of Service (ReDoS) vulnerability in the user profile API endpoint that accepts unvalidated usernames containing regex metacharacters, allowing unauthenticated remote attackers to trigger excessive CPU consumption and deny service to legitimate users. The MongoDB regex engine processes these malicious patterns inefficiently, making the platform unavailable without administrator intervention. …
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Remediation
Within 7 days: Identify all affected systems and apply vendor patches promptly. Monitor vendor channels for patch availability.
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