PuTTY wish banner-escape-codes

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summary: Interpret escape codes in pre-login banner
class: wish: This is a request for an enhancement.
difficulty: fun: Just needs tuits, and not many of them.
priority: never: We don't ever intend to fix this.

People occasionally ask for PuTTY to interpret escape codes in the banner some SSH servers send prior to authentication.

The SSH-2 authentication specification, RFC 4252, states, in the section about SSH_MSG_USERAUTH_BANNER:

If the 'message' string is displayed, control character filtering, discussed in [SSH-ARCH], SHOULD be used to avoid attacks by sending terminal control characters.

This is what PuTTY does, and as such, terminal-control sequences won't work.

Update, March 2019: while our policy on control characters hasn't changed, our implementation has. The previous filtering was very simplistic, and could mangle printable characters such as UTF-8-encoded non-ASCII characters. Now we use a more sophisticated approach that lets through characters considered printable by the current locale or terminal configuration through; so non-ASCII characters can now be displayed unmolested (if the terminal and banner message agree on the encoding, in the usual way).

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Audit trail for this wish.
(last revision of this bug record was at 2022-09-11 23:46:37 +0100)