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.

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 1.3.0 and older may incorrectly include a private tunnel identifier in the non-private details of some REST responses. This may allow an authenticated user who already has permission to access a particular connection to read from or interact with another user's active use of that same connection.

Apache Guacamole 1.2.0 and earlier do not consistently restrict access to connection history based on user visibility. If multiple users share access to the same connection, those users may be able to see which other users have accessed that connection, as well as the IP addresses from which that connection was accessed, even if those users do not otherwise have permission to see other users.

Apache Guacamole 1.1.0 and older may mishandle pointers involved inprocessing data received via RDP static virtual channels. If a userconnects to a malicious or compromised RDP server, a series ofspecially-crafted PDUs could result in memory corruption, possiblyallowing arbitrary code to be executed with the privileges of therunning guacd process.

Apache Guacamole 1.1.0 and older do not properly validate datareceived from RDP servers via static virtual channels. If a userconnects to a malicious or compromised RDP server, specially-craftedPDUs could result in disclosure of information within the memory ofthe guacd process handling the connection.

Prior to 1.0.0, Apache Guacamole used a cookie for client-side storage of the user's session token. This cookie lacked the "secure" flag, which could allow an attacker eavesdropping on the network to intercept the user's session token if unencrypted HTTP requests are made to the same domain.

A race condition in Guacamole's terminal emulator in versions 0.9.5 through 0.9.10-incubating could allow writes of blocks of printed data to overlap. Such overlapping writes could cause packet data to be misread as the packet length, resulting in the remaining data being written beyond the end of a statically-allocated buffer.