security(smime): fork upstream plugin and fix two audit findings

S-01 audited bulwarkmail/plugins/smime @ 91085a3 (2,935 lines). Nine findings, two HIGH. No backdoor and no exfiltration path anywhere in the bundle — the problems are trust-model and input-validation gaps. Full report in vnc/audits/SMIME-PLUGIN-AUDIT-2026-08-04.md. Fork is source-only. The upstream smime.zip is a 1.77 MB prebuilt bundle whose manifest reads 1.0.1 while the source reads 1.0.2, so auditing src/ would not audit what that zip installs. We build from source. Finding 1 (HIGH) — certificate substitution. maybeAutoImportSigner gated on signatureValid alone, but smimeVerify runs checkChain:false, so that only proves "signed by whoever holds this key", not that the claimed identity is real. Self-sign a cert asserting victim@example.com, send one signed message, and it was stored as the encryption target for that address — the user's next Encrypt to the victim went to the attacker. Now requires signerEmailMatch === true and !selfSigned. Both values were already computed and displayed as untrusted in the banner; only the import path ignored them. Tests for `true` explicitly so an undefined match (missing From header) fails closed. Finding 3 (MED-HIGH) — CRLF header injection. Escaping reached only Subject and attachment filename; display names, raw addresses, Message-ID, In-Reply-To, References and attachment Content-Type were emitted verbatim, and formatAddress escapes only backslash and quote. In-Reply-To/References/display names are copied from inbound mail when replying or forwarding, so the value is attacker-supplied. Sanitising inside formatHeader covers all 17 call sites by construction; the three headers assembled directly get stripCrlf explicitly. Also adds auth:observe to the manifest. The plugin registers onAfterLogout/onAccountSwitch — real hooks (lib/plugin-hooks.ts:362-363) — without declaring the permission, so under B-09 the session-key wipe would silently stop running. verify-fixes.mjs carries 19 assertions including source checks that fail if either guard is removed or a new unsanitised interpolated header appears. That last one immediately caught the interpolated smime-type Content-Type header, which manual review had dismissed as static. Finding 2 (unauthenticated CBC accepted on decrypt) is NOT fixed. This is not safe for real mail yet — sandbox accounts only. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-08-04 10:00:11 +02:00
parent e9746fcf78
commit f7e487171c
23 changed files with 4287 additions and 0 deletions
@@ -0,0 +1,47 @@
+import * as asn1js from 'asn1js';
+import * as pkijs from 'pkijs';
+import { parseCertificateDer } from './certificate-utils.js';
+import { nativeEngine } from './crypto-engine.js';
+
+/**
+ * Produce an opaque CMS SignedData wrapping the given MIME content.
+ * Content type: application/pkcs7-mime; smime-type=signed-data.
+ * Ported from lib/smime/smime-sign.ts.
+ */
+export async function smimeSign(mimeBytes, privateKey, signerCertDer, chainCertsDer = []) {
+  const signerCert = parseCertificateDer(signerCertDer);
+  const chainCerts = chainCertsDer.map((der) => parseCertificateDer(der));
+
+  const cmsSigned = new pkijs.SignedData({
+    version: 1,
+    encapContentInfo: new pkijs.EncapsulatedContentInfo({
+      eContentType: '1.2.840.113549.1.7.1', // id-data
+      eContent: new asn1js.OctetString({
+        valueHex: new Uint8Array(
+          mimeBytes.buffer.slice(mimeBytes.byteOffset, mimeBytes.byteOffset + mimeBytes.byteLength),
+        ),
+      }),
+    }),
+    signerInfos: [
+      new pkijs.SignerInfo({
+        version: 1,
+        sid: new pkijs.IssuerAndSerialNumber({
+          issuer: signerCert.issuer,
+          serialNumber: signerCert.serialNumber,
+        }),
+      }),
+    ],
+    certificates: [signerCert, ...chainCerts],
+  });
+
+  const hashAlgorithm = 'SHA-256';
+  await cmsSigned.sign(privateKey, 0, hashAlgorithm, undefined, nativeEngine());
+
+  const cms = new pkijs.ContentInfo({
+    contentType: '1.2.840.113549.1.7.2', // id-signedData
+    content: cmsSigned.toSchema(true),
+  });
+
+  const cmsBytes = cms.toSchema().toBER(false);
+  return new Blob([cmsBytes], { type: 'application/pkcs7-mime; smime-type=signed-data' });
+}