CVE-2024-21662: Argo CD Auth Bypass Vulnerability

CVE-2024-21662 Overview

CVE-2024-21662 is a critical authentication bypass vulnerability affecting Argo CD, a popular declarative GitOps continuous delivery tool for Kubernetes. This vulnerability allows attackers to effectively bypass the rate limit and brute force protections by exploiting a weakness in the application's cache-based mechanism. The flaw undermines a previous security patch for CVE-2020-8827 that was intended to protect against brute-force attacks.

Critical Impact

Attackers can bypass brute force protections by overflowing the login attempt cache, enabling accelerated credential attacks against the default admin account with potential for unauthorized access to Kubernetes deployment infrastructure.

Affected Products

• Argo CD versions prior to 2.8.13
• Argo CD versions prior to 2.9.9
• Argo CD versions prior to 2.10.4

Discovery Timeline

• 2024-03-18 - CVE-2024-21662 published to NVD
• 2025-01-09 - Last updated in NVD database

Technical Details for CVE-2024-21662

Vulnerability Analysis

This vulnerability exists in Argo CD's brute force protection mechanism, which relies on a cache to track login attempts for each user. The cache was limited to a defaultMaxCacheSize of 1000 entries, creating an exploitable condition where an attacker could overflow the cache by sending login attempts for many different usernames, thereby evicting the admin account's failed login tracking and resetting the rate limit counter.

The weakness is classified under CWE-307 (Improper Restriction of Excessive Authentication Attempts). This vulnerability is particularly dangerous as it can be combined with other attack vectors to target the default admin account, which often has elevated privileges in Kubernetes environments. The network-accessible attack vector requires no authentication or user interaction, making it easily exploitable by remote attackers.

Root Cause

The root cause lies in the insufficient size of the session manager's login attempt cache. With only 1000 entries available, an attacker can trivially generate login attempts for 1000+ unique usernames, causing the cache to evict older entries including the failed login tracking for legitimate admin accounts. This cache overflow technique effectively resets the rate limiting protection for targeted accounts.

Attack Vector

The attack can be executed remotely over the network without requiring any authentication or user interaction. An attacker targets the Argo CD login endpoint and floods the cache with login attempts using randomly generated or enumerated usernames. Once the cache size exceeds 1000 entries, the oldest entries (including any tracked admin failed attempts) are evicted. The attacker can then resume brute force attempts against the admin account with a fresh rate limit counter.

// Security patch in util/session/sessionmanager.go
// Source: https://github.com/argoproj/argo-cd/commit/17b0df1168a4c535f6f37e95f25ed7cd81e1fa4d

 	// Maximum length of username, too keep the cache's memory signature low
 	maxUsernameLength = 32
 	// The default maximum session cache size
-	defaultMaxCacheSize = 1000
+	defaultMaxCacheSize = 10000
 	// The default number of maximum login failures before delay kicks in
 	defaultMaxLoginFailures = 5
 	// The default time in seconds for the failure window

Detection Methods for CVE-2024-21662

Indicators of Compromise

• Unusually high volume of failed login attempts from single IP addresses or IP ranges
• Login attempts using a large number of distinct usernames in rapid succession
• Patterns of authentication failures followed by successful admin logins
• Sudden spikes in authentication API endpoint traffic

Detection Strategies

• Monitor authentication logs for abnormal patterns of failed login attempts across many unique usernames
• Implement external rate limiting at the network or load balancer level to catch cache overflow attempts
• Alert on authentication attempts exceeding normal baseline thresholds
• Deploy web application firewall (WAF) rules to detect and block credential stuffing patterns

Monitoring Recommendations

• Enable detailed audit logging for all Argo CD authentication events
• Configure SIEM correlation rules to detect cache overflow attack patterns
• Monitor for sequential failed logins followed by successful admin authentication
• Track unique username counts per source IP over sliding time windows

How to Mitigate CVE-2024-21662

Immediate Actions Required

• Upgrade Argo CD to version 2.8.13, 2.9.9, or 2.10.4 immediately
• Change the default admin password if still using default credentials
• Implement external rate limiting at the reverse proxy or load balancer level
• Review authentication logs for signs of prior exploitation attempts

Patch Information

Argoproj has released security patches across multiple version branches. Users should upgrade to the following patched versions:

• Version 2.8.13 for the 2.8.x branch - Commit 17b0df1
• Version 2.9.9 for the 2.9.x branch - Commit 6e181d7
• Version 2.10.4 for the 2.10.x branch - Commit cebb653

The patch increases the defaultMaxCacheSize from 1000 to 10000 entries, making cache overflow attacks significantly more difficult. For additional details, see the GitHub Security Advisory GHSA-2vgg-9h6w-m454.

Workarounds

• Deploy network-level rate limiting using a reverse proxy (nginx, HAProxy) or cloud load balancer before the Argo CD API server
• Disable local admin accounts and integrate with external SSO/OIDC providers that have their own brute force protections
• Restrict access to the Argo CD API server to trusted IP ranges using network policies
• Implement additional authentication factors (MFA) through your identity provider

# Example: Configure nginx rate limiting for Argo CD API
# Add to nginx configuration for Argo CD ingress

limit_req_zone $binary_remote_addr zone=argocd_login:10m rate=10r/m;

location /api/v1/session {
    limit_req zone=argocd_login burst=5 nodelay;
    limit_req_status 429;
    proxy_pass http://argocd-server:8080;
}