Apache Guacamole 1.5.1 and older may incorrectly calculate the lengths of instruction elements sent during the Guacamole protocol handshake, potentially allowing an attacker to inject Guacamole instructions during the handshake through specially-crafted data.

Apache Guacamole 0.9.10 through 1.5.1 may continue to reference a freed RDP audio input buffer. Depending on timing, this may allow an attacker to execute arbitrary code with the privileges of the guacd process.

Apache Guacamole 1.5.3 and older do not consistently ensure that values received from a VNC server will not result in integer overflow. If a user connects to a malicious or compromised VNC server, specially-crafted data could result in memory corruption, possibly allowing arbitrary code to be executed with the privileges of the running guacd process. Users are recommended to upgrade to version 1.5.4, which fixes this issue.