rxvt-unicode 9.25 and 9.26 are vulnerable to remote code execution, in the Perl background extension, when an attacker can control the data written to the user's terminal and certain options are set.

The "background" extension is automatically loaded if certain X resources are set such as 'transparent' (see the full list at the top of src/perl/background). So it is possible to be using this extension without realizing it.

This is accidentally fixed on version 9.30, and 9.29, it appears to not be exploitable, but only due to another bug (not a security bug). The actual bug which makes this not vulnerable on 9.30 is simply a wrong number in "onoscseq".

rxvt-unicode 9.22, rxvt 2.7.10, mrxvt 0.5.4, and Eterm 0.9.7 allow (potentially remote) code execution because of improper handling of certain escape sequences (ESC G Q). A response is terminated by a newline.