haproxy -- buffer overflow

HAProxy reports:

A flaw was reported in HAProxy where, due to a boundary error
when copying data into the trash buffer, an external attacker could
cause a buffer overflow. Exploiting this flaw could lead to the
execution of arbitrary code, however it requires non-default settings
for the global.tune.bufsize configuration option (must be set to a
value greater than the default), and also that header rewriting is
enabled (via, for example, the regrep or rsprep directives).
This flaw is reported against 1.4.20, prior versions may also be
affected.