ncompress is a suite of utilities to create and extract Lempel-Ziff-Welch (LZW) compressed archives.
Tavis Ormandy of the Google Security Team discovered a static buffer underflow in ncompress.
An attacker could create a specially crafted LZW archive, that when decompressed by a user or automated system would result in the execution of arbitrary code with the permissions of the user invoking the utility.
There is no known workaround at this time.
All ncompress users should upgrade to the latest version:
# emerge --sync
# emerge --ask --oneshot --verbose ">=app-arch/ncompress-4.2.4.1"