An issue was discovered in Oniguruma 6.2.0, as used in Oniguruma-mod in Ruby through 2.4.1 and mbstring in PHP through 7.1.5. A heap out-of-bounds write or read occurs in next_state_val during regular expression compilation. Octal numbers larger than 0xff are not handled correctly in fetch_token and fetch_token_in_cc. A malformed regular expression containing an octal number in the form of '\700' would produce an invalid code point value larger than 0xff in next_state_val, resulting in an out-of-bounds write memory corruption. An issue was discovered in Oniguruma 6.2.0, as used in Oniguruma-mod in Ruby through 2.4.1 and mbstring in PHP through 7.1.5. A stack out-of-bounds read occurs in mbc_enc_len during regular expression searching. Invalid handling of reg-greater than dmin in forward_search_range could result in an invalid pointer dereference, as an out-of-bounds read from a stack buffer. An issue was discovered in Oniguruma 6.2.0, as used in Oniguruma-mod in Ruby through 2.4.1 and mbstring in PHP through 7.1.5. A heap out-of-bounds write occurs in bitset_set_range during regular expression compilation due to an uninitialized variable from an incorrect state transition. An incorrect state transition in parse_char_class could create an execution path that leaves a critical local variable uninitialized until it's used as an index, resulting in an out-of-bounds write memory corruption. An issue was discovered in Oniguruma 6.2.0, as used in Oniguruma-mod in Ruby through 2.4.1 and mbstring in PHP through 7.1.5. A SIGSEGV occurs in left_adjust_char_head during regular expression compilation. Invalid handling of reg-greater than dmax in forward_search_range could result in an invalid pointer dereference, normally as an immediate denial-of-service condition