The x86 emulation base libraries for AMD64 emulate the x86 (32-bit) architecture on the AMD64 (64-bit) architecture.
Earlier versions of emul-linux-x86-baselibs contain a vulnerable version of zlib, which may lead to a buffer overflow.
By creating a specially crafted compressed data stream, attackers can overwrite data structures for applications that use the x86 emulation base libraries for AMD64, resulting in a Denial of Service and potentially arbitrary code execution.
There is no known workaround at this time.
All AMD64 x86 emulation base libraries users should upgrade to the latest version:
# emerge --sync
# emerge --ask --oneshot --verbose app-emulation/emul-linux-x86-baselibs