Bernd RodlerandClaude Opus 4.8
f7e487171c
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>
S/MIME plugin
End-to-end S/MIME (CMS / PKCS#7) for Bulwark Webmail, implemented as a
privileged (same-origin) plugin. All cryptography runs locally in the
browser using a bundled pkijs / asn1js / webcrypto-liner stack, with no key
material ever leaves the device.
What it does
| Capability | How |
|---|---|
| Sign outgoing mail | onComposeSend builds the MIME, wraps it in opaque CMS SignedData, and submits via api.jmap.sendRaw. |
| Encrypt outgoing mail | onComposeSend builds CMS EnvelopedData to every recipient (AES-256-GCM by default; AES-128 optional) plus the sender, then submits raw. Sign + Encrypt does proper sign-then-encrypt. |
| Verify incoming signatures | onRenderEmailBody fetches the CMS blob (api.jmap.fetchBlob), validates the signature cryptographically, checks validity dates, flags self-signed signers and signer≠From mismatches, and renders the inner body. |
| Decrypt incoming mail | onRenderEmailBody decrypts EnvelopedData with your unlocked key (RSA-OAEP, with an RSAES-PKCS1-v1_5 + 3DES/RC2 legacy fallback for old Outlook/Thunderbird mail). |
| Key management | settings-section slot: import PKCS#12 (.p12/.pfx), unlock/lock, delete, import recipient certificates, set sign/encrypt defaults. |
| Status | email-banner slot shows signature / encryption state; composer-toolbar slot has per-message Sign / Encrypt toggles. |
Security model
- Privileged tier. Declares
tier: "privileged"+crypto:full. PerresolvePluginTier, the same-origin tier is only granted to a signed, admin-approved (managed) bundle after high-risk consent. A self-uploaded copy is refused rather than downgraded; sign and ship it through the admin channel. - Keys at rest. Private keys are imported from PKCS#12 and re-wrapped with AES-256-GCM under a PBKDF2(SHA-256, 600 000) key derived from a passphrase you choose. Stored in IndexedDB; the raw key bytes are never persisted.
- Keys in use. Unlocking imports the key as a non-extractable
CryptoKey. Because the background (hooks) iframe and the visible slot iframes are same-origin, the unlocked handle is shared through a session IndexedDB store. It stays non-extractable and is wiped on app boot and on logout / account switch (configurable), mirroring the former native "in-memory, cleared on reload" behaviour. - Returned HTML still passes through the host sanitizer.
Build
cd repos/plugins/smime
npm install # pulls pkijs / asn1js / pvtsutils / webcrypto-liner + esbuild
npm run build # → dist/index.js (~1.7 MB, under the privileged cap)
npm run package # → smime.zip (manifest.json + index.js) for admin upload
The build aliases the Node crypto builtin (referenced by a dead
typeof process branch in asmcrypto.js) to a browser shim so the bundle is
self-contained.
Layout
src/
index.js entry: activate + hooks + slots (React.createElement UI)
crypto-engine.js pkijs CryptoEngine w/ 3DES/RC2 + legacy PKCS#12 PBE
certificate-utils.js X.509 parse + metadata + capability classification
mime-builder.js deterministic CRLF MIME builder + CMS RFC822 wrapper
mime-parse.js inner-MIME parser for decrypted/verified content
smime-detect.js detect CMS from Content-Type / bodyStructure / attachments
smime-sign.js CMS SignedData (opaque)
smime-encrypt.js CMS EnvelopedData
smime-decrypt.js CMS decrypt + blob normalisation + recipient matching
smime-verify.js CMS signature verification + signer status
pkcs12.js PKCS#12 import + key wrap/unlock
key-storage.js IndexedDB: key records, recipient certs, session keys
util.js uuid / hex / equality helpers
node-crypto-shim.js browser shim for the Node "crypto" builtin
The crypto modules are faithful ports of the host's lib/smime/* (the former
native pipeline), so the plugin produces byte-compatible CMS.
Note on host wiring
The onComposeSend and onRenderEmailBody hook buses and the privileged
api.jmap surface exist in the host (see lib/plugin-hooks.ts,
lib/plugin-sandbox/host-api.ts). The send/render takeover fires once the
host emits those buses from the composer and viewer (the migration that retires
the inline native path). The settings-section, composer-toolbar, and
email-banner slots are active today.