Metamail is a program that decodes MIME encoded mail.
Ulf Harnhammar discovered a buffer overflow in Metamail when processing mime boundraries.
By sending a specially crafted email, attackers could potentially exploit this vulnerability to crash Metamail or to execute arbitrary code.
There is no known workaround at this time.
All Metamail users should update to the latest version:
# emerge --sync
# emerge --ask --oneshot --verbose ">=net-mail/metamail-2.7.45.3-r1"