MongoDB
CVE-2026-21868
HIGH
Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Primary rating from GitHub Advisory · only source for this CVE.
CVSS VectorGitHub Advisory
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Lifecycle Timeline
2DescriptionGitHub Advisory
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.
AnalysisAI
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. No patch is currently available; users should implement WAF rules to filter regex metacharacters from username inputs as a temporary mitigation.
Technical ContextAI
Classified as CWE-1333 (Inefficient Regular Expression Complexity (ReDoS)). Affects the user profile API component of Flagforge. 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
RemediationAI
Fixed in version 2.3.3.. Restrict network access to the affected service where possible.
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Same technique Denial Of Service
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External POC / Exploit Code
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