fix(EXPOSED_SECRETS): redact matched secrets in finding evidence

src/__tests__/scanner.test.ts

@@ -435,6 +435,40 @@ describe('INSECURE_TRANSPORT rule', () => {
   });
 });
 
+// ─── EXPOSED_SECRETS rule ─────────────────────────────────────────────────────
+
+describe('EXPOSED_SECRETS rule', () => {
+  const OPENAI_KEY = 'sk-abcdefghijklmnopqrstuvwxyz1234567890ABCD';
+
+  it('fires when a secret-shaped value is present', () => {
+    const config: ParsedMcpConfig = { rawStrings: [OPENAI_KEY] };
+    const findings = runRuntimeRule(RuleId.EXPOSED_SECRETS, config);
+    expect(findings).toHaveLength(1);
+    expect(findings[0].ruleId).toBe(RuleId.EXPOSED_SECRETS);
+    expect(findings[0].severity).toBe(Severity.CRITICAL);
+  });
+
+  it('does NOT echo the raw secret into the finding evidence', () => {
+    const config: ParsedMcpConfig = { rawStrings: [OPENAI_KEY] };
+    const findings = runRuntimeRule(RuleId.EXPOSED_SECRETS, config);
+    const evidence = findings[0].evidence ?? '';
+    // The whole point of the rule is to get the secret rotated; reports are
+    // routinely persisted to CI logs / SARIF, so the raw value must not appear.
+    expect(evidence).not.toContain(OPENAI_KEY);
+    expect(evidence).toContain('redacted');
+    // A short, non-sensitive prefix and the length are still surfaced so the
+    // user can locate the offending value.
+    expect(evidence).toContain('OpenAI API key');
+    expect(evidence).toContain(`${OPENAI_KEY.length} chars`);
+  });
+
+  it('does not fire on a clean config', () => {
+    const config: ParsedMcpConfig = { rawStrings: ['bearer', 'https://app.example.com'] };
+    const findings = runRuntimeRule(RuleId.EXPOSED_SECRETS, config);
+    expect(findings).toHaveLength(0);
+  });
+});
+
 // ─── failOn behaviour ─────────────────────────────────────────────────────────
 
 describe('failOn config', () => {

src/rules/runtime-rules.ts

@@ -2,13 +2,28 @@ import { Finding, RuleId, Severity } from '../types.js';
 import { ParsedMcpConfig } from '../parser.js';
 import { Rule } from './index.js';
 
-const SECRET_PATTERNS: RegExp[] = [
-  /sk-[a-zA-Z0-9]{20,}/i,           // OpenAI API key
-  /ghp_[a-zA-Z0-9]{36}/i,            // GitHub PAT
-  /AKIA[0-9A-Z]{16}/i,               // AWS access key
-  /[Pp]assword\s*[=:]\s*\S{8,}/,     // Password assignment
+const SECRET_PATTERNS: Array<{ label: string; pattern: RegExp }> = [
+  { label: 'OpenAI API key', pattern: /sk-[a-zA-Z0-9]{20,}/i },
+  { label: 'GitHub personal access token', pattern: /ghp_[a-zA-Z0-9]{36}/i },
+  { label: 'AWS access key ID', pattern: /AKIA[0-9A-Z]{16}/i },
+  { label: 'hardcoded password', pattern: /[Pp]assword\s*[=:]\s*\S{8,}/ },
 ];
 
+/**
+ * Produce a non-reversible preview of a matched secret for use in finding
+ * evidence. Scan reports are routinely written to CI logs, SARIF artifacts, and
+ * GitHub Code Scanning — surfaces that are often more visible and longer-lived
+ * than the config file itself. Echoing the raw secret there would re-expose the
+ * very credential the rule is asking the user to rotate. We reveal only the
+ * leading characters (which for every pattern above are a structural prefix such
+ * as `sk-`, `ghp_`, `AKIA`, or the word `password`, not entropy) plus the total
+ * length, which is enough to locate the value without reproducing it.
+ */
+function maskSecret(value: string): string {
+  const visible = value.slice(0, Math.min(4, value.length));
+  return `${visible}…[redacted, ${value.length} chars]`;
+}
+
 export const runtimeRules: Rule[] = [
   {
     id: RuleId.INSECURE_TRANSPORT,
@@ -99,9 +114,10 @@ export const runtimeRules: Rule[] = [
       const matched: string[] = [];
 
       for (const s of rawStrings) {
-        for (const pattern of SECRET_PATTERNS) {
+        for (const { label, pattern } of SECRET_PATTERNS) {
           if (pattern.test(s)) {
-            matched.push(s.length > 60 ? s.slice(0, 57) + '...' : s);
+            // Never echo the raw secret into the report — only a masked preview.
+            matched.push(`${label} (${maskSecret(s)})`);
             break;
           }
         }
@@ -117,7 +133,7 @@ export const runtimeRules: Rule[] = [
               'The configuration file appears to contain one or more hardcoded secrets ' +
               '(API keys, tokens, or passwords). Secrets committed to config files can be ' +
               'extracted by anyone with access to the file.',
-            evidence: `Matched value(s): ${matched.slice(0, 3).join('; ')}`,
+            evidence: `Detected ${matched.length} likely secret(s): ${matched.slice(0, 3).join('; ')}`,
             remediation:
               'Remove secrets from configuration files. Use environment variables, a secrets manager ' +
               '(e.g., AWS Secrets Manager, HashiCorp Vault), or a .env file excluded from version control.',