App::Ack versions through 3.10.0 for Perl read arbitrary files via --files-from in a project .ackrc.
ack searches up the directory hierarchy from the current directory for a project .ackrc and loads its options. The project-source option blocklist in App::Ack::ConfigLoader does not include --files-from, so a project .ackrc can set it to a path whose listed files ack then reads and searches. Version 3.10.0 added --follow to the blocklist; --files-from remains accepted.
A project .ackrc committed to an untrusted repository can make ack read files outside the project and print their matching lines.
App::Ack versions before 3.10.0 for Perl allow memory exhaustion via an unbounded context value in a project .ackrc.
ack searches up the directory hierarchy from the current directory for a project .ackrc and loads its options. The -B and -C context options accepted any positive integer, and ack sized the before-context buffer to that value, so a project .ackrc setting --before-context=100000000 made ack allocate a buffer of 100 million elements.
A project .ackrc committed to an untrusted repository can abort ack with an out-of-memory condition.
App::Ack versions through 3.10.0 for Perl print unsanitised terminal escape sequences from filenames in several output modes.
When ack prints a filename whose basename contains terminal control bytes such as ANSI escape sequences, those bytes reach the terminal unchanged. Version 3.10.0 added a _safe_filename helper that sanitises the filenames printed by -f, -g, the colored match heading, and per-match lines, but the --show-types, -l/-L, and -c paths still emit the raw filename.
A file whose name embeds cursor-movement or color escapes can overwrite or recolor earlier terminal output, or be passed unchanged to a downstream consumer.