fetchmail -- heap overflow on verbose X.509 display

Matthias Andree reports:

In verbose mode, fetchmail prints X.509 certificate subject and issuer information to the user, and counts and allocates a malloc() buffer for that purpose.

If the material to be displayed contains characters with high bit set and the platform treats the "char" type as signed, this can cause a heap buffer overrun because non-printing characters are escaped as \xFF..FFnn, where nn is 80..FF in hex.

[source]