The remote-content allowlist in ToolResultSanitizationMiddleware
(`_REMOTE_CONTENT_TOOL_NAMES`) covered web_fetch / web_search /
image_search but not web_capture, which was added later. The Browserless
web_capture tool embeds the target site's `X-Response-Status` reason
phrase — free-form text controlled by whatever server is being captured
(RFC 7230 §3.1.2) — into its result message via `_target_status_warning`.
A malicious page could therefore forge a `<system-reminder>` block (or a
`--- END USER INPUT ---` boundary marker) through web_capture that would
be escaped for web_fetch, letting attacker-influenced remote content reach
the model as authoritative framework context.
Add "web_capture" to the allowlist so its result is structurally
neutralized for parity with the other remote-content tools. This extends
the same defense introduced in #4002 to the one built-in remote-content
tool it did not yet cover.
Add regression tests that build the web_capture result the way
community/browserless/tools.py does (real `_target_status_warning` +
`BrowserlessScreenshotResult`) and assert the forged tags/boundary markers
are escaped, while a benign status warning is preserved unchanged.
* fix(security): neutralize prompt-injection tags in remote tool results
User input is already neutralized for framework/injection tags, but tool
results are not. Remote content fetched by web_fetch/web_search is equally
untrusted and can carry a forged <system-reminder> block that reaches the
model verbatim as authoritative context.
Extract a shared neutralize_untrusted_tags() primitive from
InputSanitizationMiddleware and apply it to remote-content tool results
(web_fetch/web_search/image_search) via a new ToolResultSanitizationMiddleware.
Local tool output (bash/read_file) is left untouched so legitimate code/file
content is never mangled.
* test: update subagent middleware count for tool-result sanitizer
The new ToolResultSanitizationMiddleware adds one entry to the shared runtime
chain (11 -> 12). Update the subagent count assertion, use a lazy import for
neutralize_untrusted_tags so the module loads even when tests stub the
input-sanitization module, and document the new middleware in AGENTS.md.
* fix(security): address review — sanitize bare str list items; document MCP scope
- Neutralize bare str elements inside a ToolMessage content list (previously
only {type:text} dict blocks were rewritten), matching the str-in-list shape
ToolOutputBudgetMiddleware._message_text already anticipates.
- Document the name-based allowlist limitation: MCP remote-content tools
registered under arbitrary names (e.g. fetch_url) are not covered; a name
heuristic is avoided to prevent mangling local tool output, with metadata
tagging tracked as a follow-up. Add a regression test pinning this boundary.
