All unpatched versions of Argo CD starting with v1.3.0 are vulnerable to a symlink following bug allowing a malicious user with repository write access to leak sensitive YAML files from Argo CD's repo-server.
A malicious Argo CD user with write access for a repository which is (or may be) used in a Helm-type Application may commit a symlink which points to an out-of-bounds file. If the target file is a valid YAML file, the attacker can read the contents of that file.
Sensitive files which could be leaked include manifest files from other Applications' source repositories (potentially decrypted files, if you are using a decryption plugin) or any YAML-formatted secrets which have been mounted as files on the repo-server.
A patch for this vulnerability has been released in the following Argo CD versions:
Disclosed by ADA Logics in a security audit of the Argo project sponsored by CNCF and facilitated by OSTIF. Thanks to Adam Korczynski and David Korczynski for their work on the audit.