shell-quote: `quote()` command injection via a line terminator in a token after a `{ comment }` token

Impact

quote() emits a { comment } token as # followed by its text, which comments out the rest of the shell line, including the opening quote of any later string token. A line terminator in that later string ends the comment, and the rest of the string is parsed as shell input:

quote(['echo', 'ok', { comment: 'x' }, 'a\nid;#']);
// echo ok #x 'a
// id;#'

Passed to sh, bash, dash, ksh, or zsh, this runs id.

parse() emits a comment token for a # in the middle of a word (for example http://example.com/#frag), so callers that combine parse() output with another untrusted string, such as quote(parse(untrustedCommand).concat(untrustedArg)), are affected. The fix for CVE-2026-9277 rejected line terminators in the comment's own text, but not in the tokens after it.

Exploitation requires an attacker-controlled string containing a line terminator that follows a { comment } token in the same quote() call.

Patches

Fixed in v1.11.0: quote() throws a TypeError when a string after a { comment } token contains a line terminator (\n, \r, U+2028, or U+2029).

Workarounds

Drop every token after a { comment } token before calling quote(), or reject line terminators in untrusted strings. Separately, do not append other shell text after quote() output that contains a comment, since the comment swallows it.