tm_mon goes from 0-11 written dates from 1-12. It is too late to consider security
here. The worst that can happen is that tm_mon == 0 gets negative but I assume
glibc to do range checking.
Index: libmrss-0.17.1/src/mrss_parser.c
===================================================================
--- libmrss-0.17.1.orig/src/mrss_parser.c	2007-04-08 02:42:23.000000000 +0200
+++ libmrss-0.17.1/src/mrss_parser.c	2007-04-08 02:43:37.000000000 +0200
@@ -150,6 +150,7 @@
     {
       char datebuf[256];
       stm.tm_year -= 1900;
+      stm.tm_mon  -= 1;
 
       if (!data->c_locale
 	  && !(data->c_locale = newlocale (LC_ALL_MASK, "C", NULL)))