In early 2021 GNU Readline, the venerated line editing library used in everything from bash to vtysh, enabled bracketed paste mode by default. This is a significant behavior change, and while it's noted that there is a compile time option to change this default, generally you can't tell users to recompile some system library to get a feature back.
The Readline docs themselves are in the typical overly-terse GNU style so this is a quick note on how to restore the old behavior in your readline-using program. There's a function in readline that takes a string and interprets it as if it were present in the user's .inputrc file; this can be leveraged to disable bracketed paste mode like so:
char *disable_bracketed_paste = strdup("set enable-bracketed-paste off"); rl_parse_and_bind(disable_bracketed_paste); free(disable_bracketed_paste);