Aari 41b137c4c4
fix(security): block forged framework tags in the input guardrail (#4155)
* fix(security): block forged framework tags in the input guardrail

InputSanitizationMiddleware's _BLOCKED_TAG_NAMES neutralizes forged
framework tags in untrusted input, but missed soul, thinking_style, and
critical_reminders -- which the lead-agent system prompt's System-Context
Confidentiality section names as internal framework data -- and the
underscore spelling system_reminder emitted by the todo/terminal
middlewares (only the hyphen spelling was blocked). A user, or an
attacker-controlled web_fetch/web_search page via the shared
neutralize_untrusted_tags primitive, could forge these blocks. Add them.

* fix(security): cover framework authority blocks as a class, not a subset

The confidentiality section declares every framework structured tag trusted
("and all other structured tags"), so the denylist must cover the authority
blocks as a class. Add the live blocks still passing both sanitization paths
(clarification_system, self_update, response_style, citations, skill_index,
available_skills, disabled_skills, memory_tool_system, durable_context_data,
slash_skill_activation), and pin the set against drift with a test that scans
the framework source and fails when a new block is not blocked.

* fix(security): scan the whole harness for framework blocks, fail closed

The drift guard added in the previous revision scanned a hand-listed set of
source files. That is the same forgot-to-update-a-list root cause the guard was
meant to eliminate, one level up, and it failed exactly that way: tool_search.py
was not in the list, so <mcp_routing_hints> and <available-deferred-tools> —
both rendered into the lead-agent system prompt via the {deferred_tools_section}
/ {mcp_routing_hints_section} placeholders — passed both sanitization paths
unneutralized.

Replace the file list with a repo-wide scan plus an exemption set that states a
reason per tag. The point is the failure direction, not the breadth: a new
framework block anywhere in the harness now turns CI red until it is either
blocked or exempted on the record, where before a block emitted from an unlisted
file was silently unguarded.

The scan reads raw source rather than AST string literals on purpose: an
attributed block built as an f-string splits its '>' into a separate literal
chunk, so an AST-on-literals scan misses it (verified against
<consolidation_candidates>). Raw source has one comment false positive, exempted.

Exempted with reasons: leaf/wrapper elements; the memory-updater and summarizer
prompts, which are built from checkpointed state rather than the ModelRequest
this middleware rewrites, so blocking them here would be false coverage, not
protection; and the MindIE provider wire format, parsed out of model output.

The scan surfaced five further live authority blocks beyond the two reported.
Subagents reuse _build_runtime_middlewares and therefore share this denylist, so
their system-prompt blocks are in the same class: file_editing_workflow,
guidelines, output_format, working_directory. goal_continuation is a
framework-authored hidden HumanMessage injected into the lead agent.

Also loosen the scanner regex to match the tolerance of _BLOCKED_TAG_PATTERN so
an attributed block cannot hide from the guard.
2026-07-14 11:04:11 +08:00
..