Playwright MCP

All 23 findings

1. critical
   Tool `browser_evaluate` exposes a code/command execution surface· browser_evaluateexcessive agency

   `browser_evaluate` looks like it executes code or shell commands (Evaluate JavaScript expression on page or element). Arbitrary execution is the maximal authority a tool can hold -- it subsumes every other caveat, so it should never be exposed to an agent without a hard sandbox and an explicit, narrowly-scoped capability.

   fix: Do not expose raw code/shell execution to an agent. If unavoidable, run it in a disposable sandbox with no network + no host FS, gate it behind a capframe-bind capability scoped to an allow-list of commands, and require holder-of-key proof per call.

2. critical
   Tool `browser_run_code_unsafe` exposes a code/command execution surface· browser_run_code_unsafeexcessive agency

   `browser_run_code_unsafe` looks like it executes code or shell commands (Run a Playwright code snippet. Unsafe: executes arbitrary JavaScript in the Playwright server process and is RCE-equivalent.). Arbitrary execution is the maximal authority a tool can hold -- it subsumes every other caveat, so it should never be exposed to an agent without a hard sandbox and an explicit, narrowly-scoped capability.

   fix: Do not expose raw code/shell execution to an agent. If unavoidable, run it in a disposable sandbox with no network + no host FS, gate it behind a capframe-bind capability scoped to an allow-list of commands, and require holder-of-key proof per call.

3. high
   Tool `browser_drop` name implies a side effect that is not declared· browser_dropexcessive agency

   `browser_drop` looks like a side-effecting tool (its name contains a mutation verb), but its `side_effects` declaration is []. A policy synthesizer cannot produce safe rules for this tool because it cannot tell what it actually does.

   fix: Declare the tool's true side effects explicitly. If the tool is genuinely read-only, rename it to match (e.g. `email.preview` rather than `email.send`).

4. high
   Tool `browser_navigate` accepts an unconstrained URL / endpoint parameter· browser_navigatessrf surface

   The parameter(s) `url` look like URL or endpoint inputs but carry no `pattern` or `enum` constraint. An agent tricked by an indirect-injection payload can invoke this tool with an internal-service URL (e.g. `http://169.254.169.254/`) to exfiltrate cloud metadata, probe internal APIs, or pivot to services the host can reach but the caller cannot.

   fix: Constrain the URL parameter with an allow-list `enum`, or a `pattern` that restricts scheme and domain. Validate server-side against an allow-list and reject private / loopback / link-local address ranges at the HTTP client level.

5. high
   Tool `browser_tabs` accepts an unconstrained URL / endpoint parameter· browser_tabsssrf surface

   The parameter(s) `url` look like URL or endpoint inputs but carry no `pattern` or `enum` constraint. An agent tricked by an indirect-injection payload can invoke this tool with an internal-service URL (e.g. `http://169.254.169.254/`) to exfiltrate cloud metadata, probe internal APIs, or pivot to services the host can reach but the caller cannot.

   fix: Constrain the URL parameter with an allow-list `enum`, or a `pattern` that restricts scheme and domain. Validate server-side against an allow-list and reject private / loopback / link-local address ranges at the HTTP client level.

6. medium
   Tool `browser_console_messages` accepts unconstrained string input· browser_console_messagesunconstrained input

   The following string parameter(s) have no `maxLength` constraint: `filename`. Unbounded strings let an attacker stuff arbitrary payloads through the tool, including indirect-injection content.

   fix: Add a `maxLength` to each string property, or constrain with an `enum` or `pattern`. Most legitimate tool inputs fit under a few hundred bytes.

7. medium
   Tool `browser_handle_dialog` accepts unconstrained string input· browser_handle_dialogunconstrained input

   The following string parameter(s) have no `maxLength` constraint: `promptText`. Unbounded strings let an attacker stuff arbitrary payloads through the tool, including indirect-injection content.

   fix: Add a `maxLength` to each string property, or constrain with an `enum` or `pattern`. Most legitimate tool inputs fit under a few hundred bytes.

8. medium
   Tool `browser_evaluate` accepts unconstrained string input· browser_evaluateunconstrained input

   The following string parameter(s) have no `maxLength` constraint: `element`, `filename`, `function`, `target`. Unbounded strings let an attacker stuff arbitrary payloads through the tool, including indirect-injection content.

   fix: Add a `maxLength` to each string property, or constrain with an `enum` or `pattern`. Most legitimate tool inputs fit under a few hundred bytes.

9. medium
   Tool `browser_drop` accepts unconstrained string input· browser_dropunconstrained input

   The following string parameter(s) have no `maxLength` constraint: `element`, `target`. Unbounded strings let an attacker stuff arbitrary payloads through the tool, including indirect-injection content.

   fix: Add a `maxLength` to each string property, or constrain with an `enum` or `pattern`. Most legitimate tool inputs fit under a few hundred bytes.

10. medium
    Tool `browser_press_key` accepts unconstrained string input· browser_press_keyunconstrained input

    The following string parameter(s) have no `maxLength` constraint: `key`. Unbounded strings let an attacker stuff arbitrary payloads through the tool, including indirect-injection content.

    fix: Add a `maxLength` to each string property, or constrain with an `enum` or `pattern`. Most legitimate tool inputs fit under a few hundred bytes.

11. medium
    Tool `browser_type` accepts unconstrained string input· browser_typeunconstrained input

    The following string parameter(s) have no `maxLength` constraint: `element`, `target`, `text`. Unbounded strings let an attacker stuff arbitrary payloads through the tool, including indirect-injection content.

    fix: Add a `maxLength` to each string property, or constrain with an `enum` or `pattern`. Most legitimate tool inputs fit under a few hundred bytes.

12. medium
    Tool `browser_navigate` accepts unconstrained string input· browser_navigateunconstrained input

    The following string parameter(s) have no `maxLength` constraint: `url`. Unbounded strings let an attacker stuff arbitrary payloads through the tool, including indirect-injection content.

    fix: Add a `maxLength` to each string property, or constrain with an `enum` or `pattern`. Most legitimate tool inputs fit under a few hundred bytes.

13. medium
    Tool `browser_network_requests` accepts unconstrained string input· browser_network_requestsunconstrained input

    The following string parameter(s) have no `maxLength` constraint: `filename`, `filter`. Unbounded strings let an attacker stuff arbitrary payloads through the tool, including indirect-injection content.

    fix: Add a `maxLength` to each string property, or constrain with an `enum` or `pattern`. Most legitimate tool inputs fit under a few hundred bytes.

14. medium
    Tool `browser_network_request` accepts unconstrained string input· browser_network_requestunconstrained input

    The following string parameter(s) have no `maxLength` constraint: `filename`. Unbounded strings let an attacker stuff arbitrary payloads through the tool, including indirect-injection content.

    fix: Add a `maxLength` to each string property, or constrain with an `enum` or `pattern`. Most legitimate tool inputs fit under a few hundred bytes.

15. medium
    Tool `browser_run_code_unsafe` accepts unconstrained string input· browser_run_code_unsafeunconstrained input

    The following string parameter(s) have no `maxLength` constraint: `code`, `filename`. Unbounded strings let an attacker stuff arbitrary payloads through the tool, including indirect-injection content.

    fix: Add a `maxLength` to each string property, or constrain with an `enum` or `pattern`. Most legitimate tool inputs fit under a few hundred bytes.

16. medium
    Tool `browser_take_screenshot` accepts unconstrained string input· browser_take_screenshotunconstrained input

    The following string parameter(s) have no `maxLength` constraint: `element`, `filename`, `target`. Unbounded strings let an attacker stuff arbitrary payloads through the tool, including indirect-injection content.

    fix: Add a `maxLength` to each string property, or constrain with an `enum` or `pattern`. Most legitimate tool inputs fit under a few hundred bytes.

17. medium
    Tool `browser_snapshot` accepts unconstrained string input· browser_snapshotunconstrained input

    The following string parameter(s) have no `maxLength` constraint: `filename`, `target`. Unbounded strings let an attacker stuff arbitrary payloads through the tool, including indirect-injection content.

    fix: Add a `maxLength` to each string property, or constrain with an `enum` or `pattern`. Most legitimate tool inputs fit under a few hundred bytes.

18. medium
    Tool `browser_click` accepts unconstrained string input· browser_clickunconstrained input

    The following string parameter(s) have no `maxLength` constraint: `element`, `target`. Unbounded strings let an attacker stuff arbitrary payloads through the tool, including indirect-injection content.

    fix: Add a `maxLength` to each string property, or constrain with an `enum` or `pattern`. Most legitimate tool inputs fit under a few hundred bytes.

19. medium
    Tool `browser_drag` accepts unconstrained string input· browser_dragunconstrained input

    The following string parameter(s) have no `maxLength` constraint: `endElement`, `endTarget`, `startElement`, `startTarget`. Unbounded strings let an attacker stuff arbitrary payloads through the tool, including indirect-injection content.

    fix: Add a `maxLength` to each string property, or constrain with an `enum` or `pattern`. Most legitimate tool inputs fit under a few hundred bytes.

20. medium
    Tool `browser_hover` accepts unconstrained string input· browser_hoverunconstrained input

    The following string parameter(s) have no `maxLength` constraint: `element`, `target`. Unbounded strings let an attacker stuff arbitrary payloads through the tool, including indirect-injection content.

    fix: Add a `maxLength` to each string property, or constrain with an `enum` or `pattern`. Most legitimate tool inputs fit under a few hundred bytes.

21. medium
    Tool `browser_select_option` accepts unconstrained string input· browser_select_optionunconstrained input

    The following string parameter(s) have no `maxLength` constraint: `element`, `target`. Unbounded strings let an attacker stuff arbitrary payloads through the tool, including indirect-injection content.

    fix: Add a `maxLength` to each string property, or constrain with an `enum` or `pattern`. Most legitimate tool inputs fit under a few hundred bytes.

22. medium
    Tool `browser_tabs` accepts unconstrained string input· browser_tabsunconstrained input

    The following string parameter(s) have no `maxLength` constraint: `url`. Unbounded strings let an attacker stuff arbitrary payloads through the tool, including indirect-injection content.

    fix: Add a `maxLength` to each string property, or constrain with an `enum` or `pattern`. Most legitimate tool inputs fit under a few hundred bytes.

23. medium
    Tool `browser_wait_for` accepts unconstrained string input· browser_wait_forunconstrained input

    The following string parameter(s) have no `maxLength` constraint: `text`, `textGone`. Unbounded strings let an attacker stuff arbitrary payloads through the tool, including indirect-injection content.

    fix: Add a `maxLength` to each string property, or constrain with an `enum` or `pattern`. Most legitimate tool inputs fit under a few hundred bytes.