PT-2026-2108 · Flagforge · Flagforge

Tokyo-Stack · Published 2026-01-08 · Updated 2026-01-13 · CVE-2026-21868

Positive Technologies (AI Summary)

CVSS v3.1

7.5

High

Base vector

AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Name of the Vulnerable Software and Affected Versions Flag Forge versions 2.3.2 and below

Description Flag Forge is a Capture The Flag (CTF) platform susceptible to a Regular Expression Denial of Service (ReDoS) condition. The issue resides in the user profile API endpoint, /api/user/[username]. The application dynamically builds a regular expression using unescaped user input, specifically the username parameter. An attacker can exploit this by providing a specially crafted username containing regex meta-characters, such as deeply nested groups or quantifiers. This manipulation causes the MongoDB regex engine to consume excessive CPU resources, potentially leading to a Denial of Service for other users.

Recommendations Versions prior to 2.3.3 should be updated to version 2.3.3 or later. Implement a Web Application Firewall (WAF) rule to block requests containing regex meta-characters in the URL path.

Exploit

Fix

DoS

Weakness Enumeration

CWE-1333

Related Identifiers

CVE-2026-21868

GHSA-949H-9824-XMCX

Affected Products

Flagforge

References · 9

• 🔥 https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/21xxx/CVE-2026-21868.json · Exploit
• https://github.com/FlagForgeCTF/flagForge/security/advisories/GHSA-949h-9824-xmcx · Vendor Advisory
• https://nvd.nist.gov/vuln/detail/CVE-2026-21868 · Security Note
• https://osv.dev/vulnerability/CVE-2026-21868 · Vendor Advisory
• https://twitter.com/cracbot/status/2011030531480379517 · Twitter Post
• https://twitter.com/VulmonFeeds/status/2009137157630271911 · Twitter Post
• https://t.me/cveNotify/148028 · Telegram Post
• https://t.me/CVEtracker/41665 · Telegram Post
• https://twitter.com/CVEnew/status/2009149981580775652 · Twitter Post