The index_urlfetch function in index.c in Cyrus IMAP 2.3.x before 2.3.19,
2.4.x before 2.4.18, 2.5.x before 2.5.4 allows remote attackers to obtain
sensitive information or possibly have unspecified other impact via vectors
related to the urlfetch range, which triggers an out-of-bounds heap read.