Double bridging allows impersonating users by having same MXID applied to two users

[Mikaela]

Steps to reproduce and screenshots below, why are they both @freenode_mikaela[m] instead of @freenode_Michaela:matrix.org which is the real IRC nick of @mikaela:disroot.org?

1. @Mikaela:disroot.org sets nick to Michaela and joins #disroot:disroot.org and #freenode_#disroot:disroot.org
2. Freenode user sets their nick to mikaela[m]
3. @mikaela:disroot.org says something at #freenode_disroot:matrix.org and mikaela[m] something at freenode.

#disroot:disroot.org

#freenode_#disroot:matrix.org

ircs://irc.freenode.net:6697/#disroot

[kuzetsa]

As per RFC1459, a valid IRC nick ALWAYS begin with a letter (A-Z a-z), followed by:

1. -
2. [
3. ]
4. \
5. `
6. ^
7. {
8. }
9. 0-9
10. letters (A-Z a-z)

Since special characters will never occur at the beginning of a nick (assuming RFC1459 compliance) using [m] as a prefix rather than placing it at the end could 100% prevent ambiguity.

---

Edit:

Actually, what I said is false. starting a nick with [m] or nearly any other special character-type prefix is valid, it turns out. Only certain things aren't valid at the start of a nick.

I think my original point may have been - why does the IRC protocol-side nick need to contain these [m] or whatever in the first place? It is unclear why these prefixes / suffixes exist at all on the IRC protocol-side of things.