CVE-2025-29419: CTFd v3.7.6 Man-in-the-Middle Vulnerability

CVE-2025-29419 Overview

CVE-2025-29419 affects CTFd v3.7.6, an open-source platform for hosting Capture The Flag (CTF) competitions. The vulnerability exposes the application to man-in-the-middle (MITM) attacks, allowing an adversary positioned between the client and server to intercept or manipulate traffic. CTFd is widely deployed by educational institutions, corporate training programs, and security communities to run competitive cybersecurity events. Successful exploitation can compromise the confidentiality and integrity of communications between participants and the CTFd server.

Critical Impact
An attacker positioned on the network path can intercept, read, or modify traffic between CTFd users and the server, potentially exposing credentials, session data, and challenge submissions.

Affected Products

CTFd v3.7.6
Earlier CTFd 3.x releases sharing the affected transport handling (see vendor references)
Deployments that do not enforce end-to-end TLS between clients and the CTFd server

Discovery Timeline

2026-08-26 - CVE-2025-29419 published to NVD
2026-08-26 - Last updated in NVD database

Technical Details for CVE-2025-29419

Vulnerability Analysis

CTFd v3.7.6 is vulnerable to a man-in-the-middle attack against communications between clients and the CTFd server. In an MITM scenario, an attacker on the same network segment, upstream proxy, or compromised routing path can intercept requests and responses. Because CTFd handles authentication, team management, and challenge submissions over HTTP, weakness in transport protection places session tokens, credentials, and flag submissions at risk.

Public disclosure via the referenced CVE-2025-29419 analysis identifies the issue as a transport-layer weakness rather than a server-side code injection or authentication bypass. The CWE for this class of issue is typically tracked as improper certificate validation or missing encryption of sensitive data [CWE-295, CWE-311].

Root Cause

The root cause lies in insufficient enforcement of secure transport between the CTFd client and server. When TLS is not strictly required or certificate validation is not properly enforced, a network attacker can downgrade or impersonate the connection. Administrators who deploy CTFd behind unencrypted reverse proxies or without HTTP Strict Transport Security (HSTS) inherit this exposure.

Attack Vector

An attacker requires a network position between the victim and the CTFd server. This includes shared Wi-Fi, compromised routers, ARP spoofing on a LAN, or malicious upstream infrastructure. Once positioned, the attacker intercepts the plaintext session or presents a fraudulent certificate to capture credentials, hijack sessions, or tamper with scoring data. Refer to the GitHub CTFd Repository for deployment guidance and configuration references.

Detection Methods for CVE-2025-29419

Indicators of Compromise

Unexpected TLS certificate warnings or mismatched certificate fingerprints reported by CTFd users
Login sessions active from geolocations or user agents that do not match the legitimate participant
Anomalous score changes, flag submissions, or team modifications lacking corresponding legitimate client activity
Downgrade of connections from HTTPS to HTTP observed in web server or proxy logs

Detection Strategies

Inspect reverse proxy and load balancer logs for HTTP requests reaching CTFd that should have been forced to HTTPS
Monitor for duplicate session cookies used from disparate source IP addresses within short intervals
Correlate authentication events against network telemetry to identify session replay from unexpected network paths

Monitoring Recommendations

Deploy TLS certificate transparency monitoring for the CTFd hostname to detect rogue certificate issuance
Alert on requests to the CTFd application that arrive without the expected HSTS enforcement or without a valid TLS session ID
Ingest web server and application logs into a centralized analytics platform for correlation with network flow data

How to Mitigate CVE-2025-29419

Immediate Actions Required

Enforce HTTPS for all CTFd traffic and disable plaintext HTTP listeners at the reverse proxy
Enable HTTP Strict Transport Security (HSTS) with a long max-age and includeSubDomains directive
Rotate any credentials, API tokens, and session secrets that may have transited an unprotected network
Instruct participants to access CTFd only from trusted networks until mitigations are verified

Patch Information

No specific patch version is referenced in the NVD entry at the time of publication. Administrators should track upstream fixes in the GitHub CTFd Repository and upgrade beyond v3.7.6 when a release addressing this issue is available. Consult the CTFd Official Website for maintainer announcements.

Workarounds

Terminate TLS at a hardened reverse proxy such as nginx or Caddy with modern cipher suites and OCSP stapling
Bind CTFd to 127.0.0.1 so the application is only reachable through the TLS-terminating proxy
Configure the CTFd session cookie with Secure, HttpOnly, and SameSite=Strict attributes
Require VPN access for administrative endpoints to reduce the attack surface for network-adjacent adversaries

bash

# Example nginx configuration to force HTTPS and enable HSTS for CTFd
server {
    listen 80;
    server_name ctf.example.org;
    return 301 https://$host$request_uri;
}

server {
    listen 443 ssl http2;
    server_name ctf.example.org;

    ssl_certificate     /etc/ssl/certs/ctfd.crt;
    ssl_certificate_key /etc/ssl/private/ctfd.key;
    ssl_protocols       TLSv1.2 TLSv1.3;
    ssl_ciphers         HIGH:!aNULL:!MD5;

    add_header Strict-Transport-Security "max-age=63072000; includeSubDomains; preload" always;
    add_header X-Content-Type-Options "nosniff" always;

    location / {
        proxy_pass         http://127.0.0.1:8000;
        proxy_set_header   Host $host;
        proxy_set_header   X-Forwarded-Proto https;
        proxy_set_header   X-Real-IP $remote_addr;
    }
}