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feat(llm-security): v7.0.0 commit 7 — rule 18 (markdown image URL suppression)

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E2E verification against content-heavy repo (`content-claude-code`) revealed
413 entropy findings (8 HIGH / 405 MEDIUM) from markdown image CDN URLs in
JSON content indexes — e.g., `![Image 1: Title](https://www-cdn.anthropic.com/images/.../cf1dd2167fcf12f5882333ddc58a5bc1f0026952.svg)`.
These are legitimate content-repo artifacts, not credentials. The 40-char
hash segment in the CDN URL trips Shannon entropy (H=5.29 over 300 chars),
and rule 13 (inline <svg>) doesn't match since there's no literal `<svg>`
tag — the `.svg` is just a URL path suffix.

Added rule 18 `MARKDOWN_IMAGE = /!\[[^\]]*\]\(\s*https?:\/\//` — matches
`![alt](http…)` / `![alt](https…)`. Line-level (not string-level) so URL
is not over-specific.

E2E impact on `content-claude-code`:
- Before: BLOCK / 65 / 8H 437M 0L
- After:  WARNING / 56 / 3H 427M 0L

Hyperframes unchanged: BLOCK / 80 / 1C 4H 92M — real CRITICAL SQL-injection
and HIGH findings still detected.

Tests: 2 new (positive + negative fixture) bringing entropy-context to 26,
total suite 1485 → 1487.

Docs updated to "rules 11-18" and "8 new line-suppression rules".

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
This commit is contained in:
Kjell Tore Guttormsen 2026-04-19 22:37:39 +02:00
commit 765bc74f52
7 changed files with 43 additions and 9 deletions
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12
plugins/llm-security/scanners/entropy-scanner.mjs
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@ -169,6 +169,13 @@ const SQL_STATEMENT = /^\s*(?:SELECT|INSERT|UPDATE|DELETE|CREATE|ALTER|WITH|DROP
/** Error-message templates with embedded HTML/markup (throw new Error("<div>...</div>")). */
const ERROR_TEMPLATE = /(?:throw\s+new\s+(?:Error|TypeError|RangeError|SyntaxError)|new\s+Error\s*\()\s*[`'"]/;
/**
* Markdown image syntax with external URL — `![alt](https://cdn.../hash.ext)`.
* Common in JSON data indexes / article metadata; CDN URL hash segments
* produce high Shannon entropy but are not credentials.
*/
const MARKDOWN_IMAGE = /!\[[^\]]*\]\(\s*https?:\/\//;
// ---------------------------------------------------------------------------
// False-positive suppression helpers
// ---------------------------------------------------------------------------
@ -248,7 +255,10 @@ function isFalsePositive(str, line, absPath) {
// 17. Error-message templates (throw new Error("<html>...</html>"))
if (ERROR_TEMPLATE.test(line)) return true;
// 18. User-policy regex patterns from .llm-security/policy.json
// 18. Markdown image syntax with external URL — CDN hash noise in content repos
if (MARKDOWN_IMAGE.test(line)) return true;
// 19. User-policy regex patterns from .llm-security/policy.json
for (const pattern of USER_SUPPRESS_LINE_PATTERNS) {
if (pattern.test(line)) return true;
}