ncompress is a utility handling compression and decompression of Lempel-Ziv archives, compatible with the original *nix compress and uncompress utilities (.Z extensions).
compress and uncompress do not properly check bounds on command line options, including the filename. Large parameters would trigger a buffer overflow.
By supplying a carefully crafted filename or other option, an attacker could execute arbitrary code on the system. A local attacker could only execute code with his own rights, but since compress and uncompress are called by various daemon programs, this might also allow a remote attacker to execute code with the rights of the daemon making use of ncompress.
There is no known workaround at this time.
All ncompress users should upgrade to the latest version:
# emerge sync
# emerge -pv ">=app-arch/ncompress-4.2.4-r1"
# emerge ">=app-arch/ncompress-4.2.4-r1"