In the code of libical/src/libical/icaltz-util.c:find_transidx, there is a possibility of acessing the element beyond the bounds of the trans_idx.
134	  	 for (i = 0; i < num_trans; i++) {
135 	  	  	if (now < transitions [i]) {
136 	  	  	found = 1;
137 	  	  	break;
138 	  	  	}
139 	  	  }
Assume num_trans is 4, and if the now < transitions[i] is true when i is 3, in the code
147 	  	  idx = trans_idx [i];
148 	  	  types [idx].isdst ? (*dstidx = i) : (*stdidx = i);
149 	  	  	
150 	  	  if (i >= num_trans)
151 	  	  	i--;
152 	  	  else
153 	  	  	i++;
154 	  	  	
155 	  	  idx = trans_idx [i];
156 	  	  types [idx].isdst ? (*dstidx = i) : (*stdidx = i);

line 153 will be executed and then i will be 4 which is invalid and trans_idx[i](trans_idx[4]) is not a valid element in the trans_idx array.