bug#66835: Heap buffer overread in expr in regexec.c in the check_arrival_add_next_nodes function.

[Paul Eggert]

Thanks. This is a bug in the glibc regular expression matcher. It's part 
of a well known series of bugs. See, for example:

https://sourceware.org/bugzilla/show_bug.cgi?id=12896
https://sourceware.org/bugzilla/show_bug.cgi?id=17356
It's not of much practical concern since the attacker should not have 
control of B in invocations like 'expr "$A" : "$B"'.