llm-ingestion-pipeline-security/docs/LIMITATIONS.md

Honest limitations

Conceding these plainly is itself a control — it prevents the false assurance that a green scan means safe content. The README carries a summary of the highest-impact items; this is the full list, each with the mechanism.

• Structural unsolvability at the text layer. Pattern/lexicon detection is bypassable in isolation; character-injection and novel phrasings evade it. The contract (tool-less transform, capability isolation, fail-secure) carries the security — the lexicon is defense-in-depth, not a wall.
• A lone HIGH finding in trusted prose disposes to WARN, not quarantine. Under PRESET_TRUSTED_SOURCE, trust-scaling downgrades a single HIGH to WARN, and one HIGH is not "compound" (escalation needs ≥2 findings at MEDIUM+). So a HIGH injection reproduced verbatim under a trusted policy persists with a WARN. This is by design: if your "trusted" sources can carry attacker-influenced text, run them as untrusted (or add a quarantine floor).
• The quarantine floor fires at MEDIUM+, and is a no-op under the shipped upload preset. Through 0.3.0 quarantine_default floored any finding to QUARANTINE_REVIEW. That premise ("a finding is the exception") broke when the active-content detector made every ordinary markdown link a finding, so 0.3.1 raised the floor to MEDIUM+. Under PRESET_USER_UPLOAD (untrusted) a MEDIUM already escalates on trust alone, so the floor still changes no outcome there; it is live only for a caller-defined trusted policy that opts into quarantine_default. Documented so the preset is not over-read: a LOW finding on an upload now disposes WARN.
• Semantic / factual poisoning is invisible to lexicon + entropy: a false claim in clean prose carries no suspicious token. Highest impact for a wiki. The grounding module ships only a SourceGroundingCheck seam — the deterministic core does not judge semantics; a [judge] implementation must be plugged in.
• Adversarial-ML evasion can survive normalization; tokenizer mismatch between scanner and model leaves gaps. Latent / dormant memory poisoning is not judgeable at write time.
• Dormant / broken-link injection in a linked corpus (e.g. an OKF bundle): a link to a not-yet-existing target passes a per-concept write-time scan clean — the payload is planted later, when that target is written. link_graph surfaces the dangling edge as the signal, but catching the payload needs cross-write re-scan over time (the caller's disposition call).
• OKF reserved files (index.md / log.md). In a received bundle these are legitimate structure, so mode-b import_bundle scans their body and frontmatter (an injection in a directory listing is caught) rather than path-rejecting the conformant bundle. A front-end materialising individual uploads keeps the opposite rule (allow_reserved=False): a reserved basename is a listing-shadow and refused.
• A document that describes attacks is a false positive. Content documenting prompt-injection payloads (security notes, this project's own corpus) trips carrier-strip / fail-secure. At the text layer "about an attack" and "carrying an attack" are indistinguishable; such content needs a deliberate, explicitly escaped path, never a silent allow.
• Bilingual text trips the Cyrillic/Latin homoglyph rule. homoglyph:cyrillic-latin-mix (MEDIUM) flags a Latin letter adjacent to a Cyrillic look-alike, so genuine bilingual prose → MEDIUM → under untrusted → QUARANTINE_REVIEW — a real false positive for an inbox that expects multilingual content. A calibration fix is pending.
• Insider in-place edits by a trusted author are out of the untrusted-content threat model.
• Text-only. The core is text -> findings: it parses no files (no pypdf/python-docx/archive deps). Extract text first, then scan it with the high-untrust upload provenance. OCR-embedded instructions and multimodal stego are out of scope beyond the sanitizer's character-layer stripping.
• Uploaded files: only the extracted text is scanned. The dev-scoped OKF inbox showcase (tests/test_okf_inbox_uploads.py + tests/inbox_frontend.py; parsers in the [dev] extra, never core dependencies) reads .txt/.md/.csv/.docx/.pptx/.xlsx, folders and .zip, materializes an OKF bundle, then guards it. What survives extraction is out of scope: macros, OLE/embedded objects, OCR-needing images, font/render stego, encrypted files — the binary layer needs a separate scanner. The front-end owns the container threats it can see (zip-slip → path gate, zip-bomb → size cap, symlink refusal, CSV/XLSX formula-lead cells). .pdf is a deliberate concession: a top-level .pdf is refused as unsupported rather than half-scanned (a PDF parser is disproportionate for a dev showcase, and the OCR/stego it would smuggle is already out of scope). One known gap: the numeric -/+ CSV false positive (a typed XLSX numeric cell does not trip it).
• Lexicon findings are deduplicated by pattern id — count=1 and the first offset are reported, so a class matched across several channels collapses to one finding at its first location: a deliberate readability tradeoff.
• Active-content severity grades on URL shape, so a pure beacon is only LOW. Since 0.3.1 a URL that merely names a remote document (bare path, no query, no userinfo, no percent-escapes, no opaque segment) is LOW, and only a URL that can move bytes outward keeps HIGH/MEDIUM. The deliberate hole: ![x](https:// evil.test/pixel.png) on an attacker-controlled host still fetches when a renderer touches it, leaking reader IP, user-agent and timing. Grading the fetch itself would re-block every ordinary document, which is precisely the 0.3.0 regression this replaced — so beaconing is conceded, not covered.
• Short opaque URL segments slip through the same grading. Opacity is decided by entropy's primitives: base64 that decodes to text (≥20 chars), a hex id (≥32 chars), or Shannon entropy ≥4.4 at ≥24 chars. A shorter payload segment — https://evil.test/aGVsbG8gd29ybGQ — cannot be told from a name, because entropy is bounded by log2(length) at short lengths. Mitigation in depth, not in this detector: a literal credential in a URL is still caught by the LLM02 egress patterns in the same scan_output pass, whatever severity the carrier gets.
• Percent-escapes count as data-carrying — a %20 in a path is a false positive. An ordinary link with an encoded space grades as carrying and reaches QUARANTINE_REVIEW / FAIL_SECURE on an untrusted upload. Obfuscated encoding is a core exfil primitive and the ambiguous case is put on the review side deliberately; it is listed here because it is the same class of over-block that 0.3.1 fixed, in a rarer shape, and it is the first thing to re-measure against a real corpus.
• URL fragments are not graded. A fragment is never sent to the server, so it cannot carry data to the host a renderer auto-fetches, and …/overview#section is the most common shape in real documentation. The residual: a clicked link to an attacker-controlled page can have its location.hash read by that page's script, so a fragment payload on a link (not an image) is uncovered.
• Secret egress: base64-wrapped is caught, hex-wrapped is not. The output gate decodes base64 blobs and re-scans the plaintext, so a base64-wrapped secret surfaces as decoded:egress:*. entropy exposes decoded plaintext for base64 only, so hex (and other encodings, or nested wraps) is a deliberate boundary — decode the transport layer first if you need it scanned.

The six documented gaps (tracked by the coverage matrix)

These are asserted to still hold by tests/test_coverage_matrix.py — a closed gap fails the test, forcing this doc to be updated:

1. Hex-wrapped secret egress — entropy decodes base64 only (above).
2. Semantic / factual poisoning — invisible to token analysis (above).
3. A lone HIGH in trusted prose → WARN — the §4.7 trust-scaling design (above).
4. Lexicon dedup (count=1) — first offset only, by design (above).
5. Pure beaconing — a bare-path remote image on a hostile host is LOW (above).
6. Short opaque URL segment (<24 chars) — below what entropy can resolve (above).

Out-of-scope (documented boundary)

Embedding/vector-layer defenses (OWASP LLM08, downstream of persist); multimodal steganography; query-time / runtime guardrails; semantic factuality verification.