ZeptoClaw: Email Sender Spoofing to bypass Header-Only From Allowlist Validation

Summary

### Summary The email channel authorizes senders based on the parsed `From` header identity only. If upstream email authentication/enforcement is weak (for example, relaxed SPF/DKIM/DMARC handling), an attacker can spoof an allowlisted sender address and have the message treated as trusted input. ### Details Relevant code paths: - `src/channels/email_channel.rs:311` extracts sender identity from parsed message headers: - `let from = parsed.from() ... a.address() ...` - `src/channels/email_channel.rs:328` authorizes using that `from` value: - `if !self.is_sender_allowed(&from) { ... }` - `src/channels/email_channel.rs:87` onward (`is_sender_allowed`) performs allowlist/domain matching against the same header-derived value. - There is no in-channel validation of sender authenticity indicators such as SPF/DKIM/DMARC results before allowlist trust decisions. Result: - Trust decision is based on a potentially spoofable header field unless mailbox/provider-side anti-spoofing controls are strong and enforced. ### PoC 1. Configure email channel with strict sender allowlist: - `channels.email.enabled = true` - `channels.email.allowed_senders = ["[email protected]"]` - `channels.email.deny_by_default = true` 2. Ensure the monitored mailbox accepts or forwards a spoofed message (for testing, use a local SMTP path that does not enforce sender authentication strongly). 3. Send an email to the monitored inbox with forged header identity: ```bash python - <<'PY' import smtplib from email.message import EmailMessage msg = EmailMessage() msg["From"] = "[email protected]" # forged trusted sender msg["To"] = "[email protected]" msg["Subject"] = "forged control message" msg.set_content("FORGED EMAIL CONTENT") # Example test SMTP endpoint with smtplib.SMTP("127.0.0.1", 25) as s: s.send_message(msg) PY ``` 4. Wait for IMAP fetch/IDLE processing. 5. Observe the message is accepted as allowlisted sender `[email protected]` and published as inbound channel input. ### Impact - Vulnerability type: sender identity spoofing risk due to header-based authorization. - Affected deployments: those using email channel allowlists where upstream anti-spoof controls are weak, misconfigured, or bypassed. - Security effect: - Spoofed `From` headers may bypass logical sender allowlist. - Malicious content can enter trusted automation/agent flows as if sent by authorized identities. - Risk is reduced in environments with strict SPF/DKIM/DMARC enforcement and strong inbound mail hygiene, but not eliminated at application layer. ### Patch Recommendation Add a sender-authentication gate in `src/channels/email_channel.rs` immediately after parsing `from` (`src/channels/email_channel.rs:311`) and before allowlist enforcement (`src/channels/email_channel.rs:328`). The gate should require trusted SPF/DKIM/DMARC evidence with domain alignment (for example, `DMARC=pass`, or aligned SPF/DKIM pass) before `is_sender_allowed` is evaluated. For backward compatibility, add a configurable mode in `EmailConfig` (for example, `sender_verification_mode`), but recommend hardened settings in production: `dmarc_aligned`, exact-address allowlists, and `deny_by_default=true`.