Due to incorrect use of integer types and missing overflow checks in
the tre_tnfa_run_parallel function's buffer overflow logic, the TRE
regex implementation (both original version and the one used in musl
libc) are subject to integer overflows in buffer size computation.

If the caller passes to regcomp a regular expression whose internal
representation requires a large number of states and/or a large number
of tags, too little space will be allocated during regexec, resulting
in out-of-bound memory writes.

An attacker who controls the regular expression and/or the string
being searched can potentially exploit these writes to achieve
controlled heap corruption.

References:

http://seclists.org/oss-sec/2016/q4/183