YAMCS User Enumeration - Information Disclosure via Authentication Response Analysis

Vulnerability Overview

YAMCS yamcs-core 5.12.7 suffers from a user enumeration flaw in its authentication mechanism. The vulnerability stems from inconsistent or distinguishable server responses when processing login attempts with valid versus invalid usernames. This is a classic information disclosure vulnerability (CWE-204: Observable Timing Discrepancy) where the application inadvertently reveals whether a user account exists through response timing, error messages, or HTTP status code variations.

Proof-of-Concept Significance

The disclosed PoC demonstrates that an unauthenticated attacker can systematically enumerate valid user accounts without requiring credentials. This precondition—network access to the YAMCS instance—is typically achievable in most operational environments. The reliability of user enumeration attacks is generally high, as they exploit fundamental authentication response patterns that are difficult to completely eliminate.

Detection Guidance

Defenders should monitor for:

• Pattern analysis: Multiple rapid authentication failures from a single source followed by systematic username variations
• Log indicators: Authentication logs showing consistent response deltas (timing, status codes) correlating with known vs. unknown usernames
• IDS/WAF signatures: Detecting brute-force patterns against /login or authentication endpoints with iterating parameter values
• Behavioral anomalies: High-velocity login attempts from single IPs testing sequential or dictionary-based usernames

Mitigation and Patching

Immediate actions:

1. Upgrade YAMCS yamcs-core to a patched version (>5.12.7) if available
2. Implement consistent response times and messages for both valid and invalid usernames
3. Deploy rate limiting on authentication endpoints (e.g., 5 attempts per minute per IP)
4. Enable account lockout policies after repeated failed attempts
5. Implement CAPTCHA on authentication forms after threshold failures
6. Restrict network access to YAMCS instances via firewall/VPN

Configuration hardening:

• Disable detailed error messages in production
• Implement generic authentication failure responses
• Enable comprehensive authentication audit logging

Risk Assessment

Likelihood: Medium-High. User enumeration is a low-barrier attack; it requires only network access and basic scripting capability, making it attractive to reconnaissance-phase attackers. Threat actor interest: High—this typically precedes credential stuffing, targeted phishing, or brute-force attacks. YAMCS systems managing spacecraft/satellite operations (its primary use case) are high-value targets for state-sponsored and criminal actors seeking operational disruption or intelligence.