Postmark MCP Server Package Hijacked for Email Exfiltration

# Postmark MCP Server Package Hijacked for Email Exfiltration

https://gcdradar.vercel.app/incidents/postmark-mcp-server-package-hijacked-for-email-exfiltration · AIR-2026-0346 · closed 2026-04-14

- Lane: Supply chain
- Severity: 3 (Confirmed exploitation)
- Fix status: Fix status unknown
- First reported: 2026-03-31 (happened 2025-09)
- AI role: Attack on AI
- Products: Postmark MCP

## Summary

Threat actors performed a malicious rugpull update on a popular npm package for an MCP server. The compromised server successfully exfiltrated user emails through AI agents.

## What to do

No action recorded; read the sources below and the vendor's advisory.

## Latest updates

- 2026-03-31: First Malicious MCP in the Wild: The Postmark Backdoor That's Stealing Your Emails (https://koi.ai/blog/postmark-mcp-npm-malicious-backdoor-email-theft)
- 2026-03-31: Poisoned Postmark MCP Server Email Exfiltration (https://atlas.mitre.org/studies/AML.CS0053)

## Sources

- 2026-03-31 MITRE ATLAS: Poisoned Postmark MCP Server Email Exfiltration https://atlas.mitre.org/studies/AML.CS0053
- 2026-03-31 koi.ai: First Malicious MCP in the Wild: The Postmark Backdoor That's Stealing Your Emails https://koi.ai/blog/postmark-mcp-npm-malicious-backdoor-email-theft

Verify against the vendor's advisory before changing production. Data CC BY-SA 4.0, https://gcdradar.vercel.app.