libregf through 20260526 contains a heap out-of-bounds read in libregfvalueitemreadvaluedata() because it bounds value data size without subtracting the 4-byte old-format cell offset. Attackers can supply a crafted version 1.0/1.1 REGF hive with a value data cell ending its hive bin to leak adjacent heap bytes or crash parsers like regfexport and plaso.