Argo CD is a declarative, GitOps continuous delivery tool for Kubernetes. Prior to versions 2.8.13, 2.9.9, and 2.10.4, an attacker can effectively bypass the rate limit and brute force protections by exploiting the application's weak cache-based mechanism. This loophole in security can be combined with other vulnerabilities to attack the default admin account. This flaw undermines a patch for CVE-2020-8827 intended to protect against brute-force attacks. The application's brute force protection relies on a cache mechanism that tracks login attempts for each user. This cache is limited to a `defaultMaxCacheSize` of 1000 entries. An attacker can overflow this cache by bombarding it with login attempts for different users, thereby pushing out the admin account's failed attempts and effectively resetting the rate limit for that account. This is a severe vulnerability that enables attackers to perform brute force attacks at an accelerated rate, especially targeting the default admin account. Users should upgrade to version 2.8.13, 2.9.9, or 2.10.4 to receive a patch.

References:

https://argo-cd.readthedocs.io/en/stable/security_considerations/#cve-2020-8827-insufficient-anti-automationanti-brute-force
https://github.com/argoproj/argo-cd/commit/17b0df1168a4c535f6f37e95f25ed7cd81e1fa4d
https://github.com/argoproj/argo-cd/commit/6e181d72b31522f886a2afa029d5b26d7912ec7b
https://github.com/argoproj/argo-cd/commit/cebb6538f7944c87ca2fecb5d17f8baacc431456
https://github.com/argoproj/argo-cd/security/advisories/GHSA-2vgg-9h6w-m454