The remote host is affected by the vulnerability described in GLSA-200507-19 (zlib: Buffer overflow)
zlib improperly handles invalid data streams which could lead to a buffer overflow. Impact
By creating a specially crafted compressed data stream, attackers can overwrite data structures for applications that use zlib, resulting in arbitrary code execution or a Denial of Service. Workaround
There is no known workaround at this time.
All zlib users should upgrade to the latest version:
# emerge --sync
# emerge --ask --oneshot --verbose ">=sys-libs/zlib-1.2.3"