gzip (GNU zip) is a popular compression program. The included zgrep utility allows you to grep gzipped files in place.
The gzip and gunzip programs are vulnerable to a race condition when setting file permissions (CAN-2005-0988), as well as improper handling of filename restoration (CAN-2005-1228). The zgrep utility improperly sanitizes arguments, which may come from an untrusted source (CAN-2005-0758).
These vulnerabilities could allow arbitrary command execution, changing the permissions of arbitrary files, and installation of files to an aribitrary location in the filesystem.
There is no known workaround at this time.
All gzip users should upgrade to the latest stable version:
# emerge --sync
# emerge --ask --oneshot --verbose ">=app-arch/gzip-1.3.5-r6"