What the vulnerability does
01Description
Vim is an open source, command line text editor. From 9.1.0011 to before 9.2.0137, Vim's NFA regex compiler, when encountering a collection containing a combining character as the endpoint of a character range (e.g. [0-0\u05bb]), incorrectly emits the composing bytes of that character as separate NFA states. This corrupts the NFA postfix stack, resulting in NFA_START_COLL having a NULL out1 pointer. When nfa_max_width() subsequently traverses the compiled NFA to estimate match width for the look-behind assertion, it dereferences state->out1->out without a NULL check, causing a segmentation fault. This vulnerability is fixed in 9.2.0137.
