Harden forward handler: SNS signature verification, rate limiting, atomic cap#11
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Harden forward handler: SNS signature verification, rate limiting, atomic cap#11
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…omic cap 1. SNS signature verification (HIGH): Add sns-validator to cryptographically verify all incoming SNS messages before processing. Prevents forged notifications that could inject messages into any inbox or trigger arbitrary forwarding. 2. Subdomain forward rate limiting (MEDIUM): Cap at 200 forwards/hr per subdomain, logged to SendLog. Prevents catch-all abuse as an open relay for externally-originated spam. 3. Atomic message cap (LOW): Wrap count+create in a Prisma $transaction to prevent concurrent emails from racing past the 500 message limit. Co-Authored-By: Claude Opus 4.6 <[email protected]>
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| const subdomainName = recipientDomain.replace(`.${DOMAIN}`, ''); | ||
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| // Rate-limit forwards per subdomain to prevent open relay abuse | ||
| const oneHourAgo = new Date(Date.now() - 60 * 60 * 1000); |
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Rate limit check on line 253 is not atomic with sendLog.create() on line 287, allowing concurrent requests to bypass the 200/hr forward limit
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Summary
Security audit found 3 vulnerabilities in the forward handler. All fixed.
1. SNS notification forgery (HIGH) — Forward handler only checked TopicArn, not cryptographic signature. An attacker who knew the ARN could forge notifications to inject messages into any inbox or trigger arbitrary forwards.
Fix: Added
sns-validatorpackage. All SNS messages are now cryptographically verified against Amazon's signing certificate before processing. Forged POSTs get 403.2. Catch-all open relay (MEDIUM) — A subdomain owner could set
catchAllForwardToto a victim's address, then external spam sent to*@attacker.x402email.comgets relayed through SES for free. Risks SES account suspension.Fix: Rate-limit subdomain forwards to 200/hr. Each forward logged to SendLog with a synthetic
[email protected]fromEmail for counting. Excess forwards are dropped with a log message.3. Message cap race condition (LOW) — TOCTOU between count check and message create. Concurrent SNS notifications could exceed the 500 message cap.
Fix: Wrapped count+create in a Prisma
$transactionfor atomicity.Test plan
[email protected]— should still be received (SNS signature valid)/api/inbox/forwardwith fake TopicArn gets 403🤖 Generated with Claude Code