# 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. - **OKF frontmatter is a restricted grammar, and a one-key block-sequence item is silently misparsed.** Gate T2 accepts a line-oriented subset deliberately — full YAML is a larger parse-attack surface than a write-time gate needs. Nested mappings and flow collections (`[a, b]`, `{k: v}`) are *rejected outright*, which fails secure. **All three routes to a mapping fail, each on a different rule** — flow (`{k: v}`) on the disallowed value-start indicator, block (`k:\n sub: v`) on the nested-mapping check, and dotted keys (`k.sub: v`) on the key pattern — so the mapping *class* has no expressible form, rather than one form being preferable to another. What survives is scalars and flat lists of strings. The defect is between those two outcomes: a block sequence whose items carry exactly **one** key parses "successfully" into the wrong type — `sources:\n - uri: https://e.com/a` yields the **string** `'uri: https://e.com/a'`, not a mapping, while the same list with two keys per item hard-rejects. A pointer can therefore ride through in a key the `resource` allowlist never inspects (`attester:\n - resource: attesters/sql_equality.py` → WARN), whereas a top-level `resource:` with a relative path correctly fails secure. The shape is not conformant OKF, so a well-formed bundle will not produce it; a malformed or hostile one can, and mode-b `import_bundle` writes the merged concept verbatim. Note the three block-list shapes are *not* one case: flat scalars parse correctly, one key per item misparses silently, two keys per item hard-rejects. - **T2 constrains import, not emission.** The frontmatter grammar runs on `okf.import_bundle` (door C) only — `parse_frontmatter` is referenced nowhere in the door A/B persist path, so frontmatter that fails secure on import passes `screen_output` unremarked. The grammar therefore bounds what a consumer can *receive*, never what a producer can *emit*. Verified identical on 0.2.0 and 0.3.1. - **Consequence: an OKF v0.2 concept cannot traverse the external-import path.** Both of v0.2's backward-breaking migration targets are nested — `timestamp` → `generated.at`, and body `# Citations` → a `sources` block list of mappings — so a conformant v0.2 concept fails secure at the frontmatter gate. This is the correct direction but it is a compatibility wall, not a policy: v0.2 support requires a deliberate parse-safety decision about widening the grammar, and the dangling-or-substituted `executor`/ `attester` pointer question only becomes live once that decision is made. - **A persist gate cannot cover execution risk.** OKF v0.2 introduces concepts whose purpose is to *name code to be run* (`runtime`, `executor.resource`, `attester.resource`). This library answers "is this safe to **store**"; executable code carries its risk at **run**. A file that is harmless to persist can be harmful to point at. Upstream defers the attester ABI and sandboxing to a future revision, so there is no runtime contract to gate against — the execution boundary is *unowned* across the stack rather than covered by anyone's roadmap, and no tightening of a write-time scanner would change that. - **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. **It is a non-ASCII-language tax, and that is the finding.** Three consumer corpora measured it (2026-07-25/26). The two English ones found zero — 0 of 347 external URLs in a 527-document vendor-docs corpus, 0 of 81 in a capture store. The third, a 389-file Norwegian/Microsoft reference corpus, found 10 distinct real escapes and **every one of them Norwegian**: `%C3%B8` and `%C3%A5` are simply *ø* and *å* in UTF-8, and legal/government sources turn titles into paths (`lovdata.no/…/kap2/%C2%A710`). "Accepted false positive" reads differently as "URLs in your own language grade above LOW". **Two distinct axes, which an earlier revision of this file conflated.** For *third-party link* corpora — URLs an ingester collects from other people's sites — language does predict: the corpus of Norwegian legal/government sources carried escapes where two link corpora of mostly English-language domains carried none. For *generated paths* the predictor is not language but **slugger class**: a whitelist slugger (`[^a-z0-9]+ → "-"`) cannot emit an escape in any language, because it discards the character before anything encodes it — measured structurally, not statistically, by a consumer whose content is Norwegian and whose slugger output is `"Løkkene i produksjonslinja" → "l-kkene-i-produksjonslinja"`. A path built with `encodeURIComponent` produces escapes systematically the moment titles are non-ASCII. So non-ASCII language is a *confounder* for encode-vs-whitelist, and the slugger class is the testable thing at a consumer — a one-line code read, not a corpus census. That question is still open for the one consumer whose slugger we have not seen. One sub-class worth separating: `{tenant}`/`{agent-id}` template placeholders in API code samples encode to `%7B`/`%7D` (26 of that corpus's 36 hits — an artifact of harvesting, not of prose). - **A percent-escaped path also defeats tokenization, which feeds the entropy branch.** `%` is not in the separator class, so `NSMs%20Grunnprinsipper%20for%20IKT` is one 34-character token where the same title with literal spaces would be four short ones. Measured at H=4.04 — under the 4.4 floor, and moot in practice because the `%` rule already disqualifies the URL. It is recorded because it means the length floor does less work in non-ASCII paths than the calibration assumed. - **Legitimate CDN content-asset ids trip the hex branch, permanently.** A ≥32-char hex path segment is opaque by design, and several public CMSes mint asset URLs that way (measured: 9 distinct on `regjeringen.no`, `ks.no`, `datatilsynet.no`). This is the "legitimate build hash or doc id" case the calibration predicted, now confirmed present in the field. The class does not decay — it is how those systems generate URLs — so it is a standing false positive rather than a transient one. The branch is otherwise precise (no other false positives in 2401 distinct URLs) and stays. - **A non-empty query is graded as data-carrying — the over-block that actually occurs in the field.** Three corpora have now measured it, and each found a *disjoint* benign population: **(1)** 16 of 16 query-carrying external URLs in a vendor-docs corpus were publisher-authored campaign tracking (`utm_*` on the publisher's own domains); **(2)** 28 of 28 in a capture store were content identity (`?v=`, `?channel_id=`, `?all=true`) where the parameter *is* the resource; **(3)** 149 of 1694 distinct `learn.microsoft.com` URLs in a reference corpus carried `?view=`, Microsoft Learn's own documentation-version selector, plus 23 `?api-version=`. **No parameter-level remedy covers any two of them, let alone all three:** an allowlist keyed on tracking-parameter names resolves (1) entirely and (2) and (3) not at all; stripping the query is lossless for (1), dereferences nothing for (2), and silently changes *which document is cited* for (3) — the worst failure mode of the three, because the result stays plausible. This is a settled constraint on any future middle tier, not a hypothesis. The cost is bounded — a query-carrying *link* is MEDIUM, so it disposes QUARANTINE_REVIEW under `PRESET_USER_UPLOAD` and WARN under `PRESET_TRUSTED_SOURCE`: held or warned, never hard-failed (pinned in `tests/test_wiring.py`, because both consumers inferred a hard block rather than running it). An *image* keeps HIGH, and that is the carrier where this would bite — the two corpora that reported a carrier breakdown contained zero remote images and the third did not report one, so the image row of this limitation remains unmeasured in the field. - **Raw HTML with a *relative* URL attribute is HIGH, though it can reach no attacker-controlled host.** The markdown paths test for an external target before flagging; the raw-HTML path deliberately does not, because an active element needs no URL at all (an `on*=` handler executes on its own). That reasoning covers event handlers but over-reaches on the URL-attribute branch: an element outside the active name set carrying `href="/en/agent-sdk/quickstart"` — an internal doc route — grades HIGH. Measured on a vendor-docs corpus, where it lands on MDX components: `` fires this way, and `` fires on the *name* branch alone because names are lower-cased and `frame` is in the active set — legacy HTML framesets, which appear in essentially no modern documentation, while `Frame` is a common component name. Case is not an available discriminator: HTML is case-insensitive, so PascalCase cannot be treated as "component, not tag". - **Raw-HTML findings count end tags.** `` is active by name on its own, so a corpus census that counts only opening tags understates what this detector reports by roughly the ratio of closing to opening active tags (measured at 1.6× on one corpus). Severity and finding count are unaffected — the class collapses to one finding — but the `count` field is not a document count. - **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.