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fix(injection): E16 ASCII fast-path + UNI-003 expectation update (v7.2.0)

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Two follow-up fixes after E16 + E17 landed:

1. foldHomoglyphs ASCII fast-path
   - scanForInjection calls foldHomoglyphs on every scan (raw + normalized).
   - Pre-fix: NFKC normalization runs unconditionally, even on pure
     ASCII inputs where it's a no-op.
   - Result: benchmark.test.mjs timed out at 120s on the full suite.
   - Fix: charCodeAt sweep for >=128, short-circuit return s when
     all ASCII. NFKC and HOMOGLYPH_MAP iteration only run when
     non-ASCII chars are present (the actual attack case).
   - Verified: benchmark.test.mjs passes within timeout.

2. Attack-scenario UNI-003 expectation
   - Pre-E16: "Homoglyph Cyrillic-Latin mixing" payload triggered only
     a MEDIUM "obfuscation present" advisory (exit 0, stdout match
     "MEDIUM").
   - Post-E16: the same payload is folded to Latin BEFORE pattern
     matching, so it now matches CRITICAL "ignore previous instructions"
     and blocks (exit 2).
   - This is the intended v7.2.0 behavior — not a regression. Updated
     expectation: exit_code 2, stdout_match "block". Renamed scenario
     to "now blocked via E16 fold, v7.2.0".

Suite: pre-compact-scan flake remains (perf-budget under load,
passes isolated). All other tests green.
This commit is contained in:
Kjell Tore Guttormsen 2026-04-29 14:44:41 +02:00
commit 6073952b97
2 changed files with 15 additions and 3 deletions
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6
plugins/llm-security/knowledge/attack-scenarios.json
View file

@ -881,7 +881,7 @@
},
{
"id": "UNI-003",
"name": "Homoglyph Cyrillic-Latin mixing (MEDIUM)",
"name": "Homoglyph Cyrillic-Latin mixing (now blocked via E16 fold, v7.2.0)",
"input": {
"session_id": "red-team",
"message": {
@ -890,8 +890,8 @@
}
},
"expect": {
"exit_code": 0,
"stdout_match": "MEDIUM"
"exit_code": 2,
"stdout_match": "block"
}
},
{

12
plugins/llm-security/scanners/lib/string-utils.mjs
View file

@ -451,11 +451,23 @@ const HOMOGLYPH_MAP = Object.freeze({
* Norwegian/Polish/German/etc. text is NOT affected — characters like
* æ, ø, å, é, ñ, ü, ö, ä are not in HOMOGLYPH_MAP.
*
* Performance: pure-ASCII inputs short-circuit before NFKC, since NFKC is
* a no-op on ASCII and HOMOGLYPH_MAP only contains non-ASCII keys.
* scanForInjection calls this on every scan; the fast-path keeps the
* common-case overhead near zero.
*
* @param {string} s
* @returns {string}
*/
export function foldHomoglyphs(s) {
if (!s) return s;
// Fast path: pure ASCII has nothing to fold and NFKC is identity.
// charCodeAt is cheaper than iterating codepoints.
let asciiOnly = true;
for (let i = 0; i < s.length; i++) {
if (s.charCodeAt(i) > 127) { asciiOnly = false; break; }
}
if (asciiOnly) return s;
const normalized = s.normalize('NFKC');
let out = '';
for (const ch of normalized) {