Two inbound-mail handlers act on a privileged effect without verifying that the sender is the operator, while a sibling handler in the same repo does. The higher-impact one: any external email routed to the bridge inbox causes the dispatcher to resume the operator's Claude Code session with permissionMode: 'bypassPermissions', embedding the attacker-controlled from/subject/preview verbatim into the prompt the resumed agent reads — an indirect prompt injection into a fully-privileged agent (Bash/Write/Edit/WebFetch + the agenticmail MCP toolbelt) running as the operator's OAuth identity. The sibling operator-query email-reply hook gates the same untrusted-From provenance with isOperatorReplySender(replyFrom, config.operatorEmail) (fail-closed); the bridge-wake path — a strictly higher-privilege effect — has no equivalent.
// affected code (current head, commit b95f52e)Untrusted provenance: external inbound email enters at packages/api/src/routes/inbound.ts:41 (POST /mail/inbound); the x-inbound-secret authenticates only the relay->API hop, not the external sender, so from/subject/preview are attacker-controlled.
Privileged sink (bridge-wake, bypassPermissions):
- packages/claudecode/src/dispatcher.ts:2040 handleBridgeMail extracts subject/from/preview (:2045-2049) and calls planBridgeWake({ session, mail: { ..., from, preview } }) (:2052) with NO sender check — routing keys only on session freshness (skip-live / escalate / resume).
- planBridgeWake -> packages/core/src/host-bridge.ts:141 composeBridgeWakePrompt embeds the untrusted from/subject/preview (preview sliced to 600 chars at :144) verbatim into the prompt.
- packages/claudecode/src/bridge-wake.ts:103 resumeBridgeSession runs the prompt via the Claude Code SDK with permissionMode: 'bypassPermissions' against the operator's last session (resume + same mcpServers).
Guarded sibling (same class, authenticated): packages/api/src/routes/inbound.ts:102 rejects an operator-query email reply unless isOperatorReplySender(replyFrom, config.operatorEmail) (def packages/core/src/phone/realtime-tools.ts:999, fail-closed when no operatorEmail), with a v0.9.53 security-review comment (inbound.ts:93-100) stating inbound mail provenance is untrusted and an emailed answer is only honored when its From matches the configured operator. The Telegram sibling likewise gates on operatorChatId. The bridge-wake path ignores this exact lesson.
Secondary instance (same root cause): packages/core/src/gateway/manager.ts:261 tryProcessApprovalReply releases a held outbound email on an "approve" reply matched only by In-Reply-To / notificationmessageid, with no sender check — again unlike the isOperatorReplySender sibling.
// impactIn a configured headless-bridge deployment (operator uses the CLI so a host-session is saved; session fresh arbitrary OS command execution, filesystem read/write, and exfiltration under the operator's OAuth identity. The auth gap (no sender check on the bridge path) is structural and unconditional; the impact realization is config-conditional and depends on the resumed model following injected instructions.
// proof of concept (static / request-difference; dynamic on operator's own setup only)Static: the from/subject/preview extracted at dispatcher.ts:2045-2049 flow into composeBridgeWakePrompt (host-bridge.ts:141) and resumeBridgeSession (bridge-wake.ts:103) with no interposed sender check, while the sibling inbound.ts:102 has one — the same untrusted-From provenance is authenticated on one privileged email path and not on the higher-privileged one. Dynamic (own instance only): with a configured bridge + fresh host-session, send mail from a non-operator address into the bridge inbox whose subject/preview contains a benign instruction writing a fresh CSPRNG marker; observe the resumed bypassPermissions session act on it. Use only your own instance; do not target third-party deployments.
// suggested fixMirror the guarded sibling: before any bypassPermissions resume (dispatcher.ts handleBridgeMail, before planBridgeWake), require trusted provenance — an internal sub-agent wake OR isOperatorReplySender(from, config.operatorEmail); otherwise deliver the mail normally but do NOT resume. Reuse the existing exported isOperatorReplySender from @agenticmail/core so the two privileged email paths share one authentication helper. Defense-in-depth: in composeBridgeWakePrompt, wrap the untrusted fields in explicit untrusted-data delimiters and drop bypassPermissions for mail-triggered resumes whose provenance is not the operator. Apply the same sender gate to tryProcessApprovalReply (manager.ts:261).
// affected versionsPresent on current HEAD (core 0.9.42 / claudecode 0.2.38, commit b95f52e). No fix retrofits the sender check onto bridge-wake.
// severity (honest, both ways)HIGH, plausibly CRITICAL in a configured headless-bridge deployment. Ceiling ~9.0 (unauthenticated external sender -> operator-privileged code execution). Floor ~7.0: the auth gap is unconditional, but full impact requires (1) a fresh <24h host-session, (2) external mail routed to the bridge inbox, (3) the resumed model obeying injected instructions (non-deterministic). Not a deterministic RCE primitive. CWE-306 (missing authentication for the privileged action) + CWE-77/CWE-94 (injected instructions realized as command execution). Novelty: the two existing agenticmail advisories (CVE-2026-50287 MCP missing-auth; CVE-2026-47255 storage SQL) do not cover this sink. Please rate per your deployment assumptions.
CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
- Attack vector
- Network
- Attack complexity
- High
- Attack requirements
- None
- Privileges required
- None
- User interaction
- None
- Confidentiality (vulnerable system)
- None
- Integrity (vulnerable system)
- High
- Availability (vulnerable system)
- None
- Confidentiality (subsequent systems)
- None
- Integrity (subsequent systems)
- None
- Availability (subsequent systems)
- None