CVE-2025-34072

Anthropic Slack MCP Server Data Exfiltration via Link Unfurling

A data exfiltration vulnerability exists in Anthropic’s deprecated Slack Model Context Protocol (MCP) Server via automatic link unfurling. When an AI agent using the Slack MCP Server processes untrusted data, it can be manipulated to generate messages containing attacker-crafted hyperlinks embedding sensitive data. Slack’s link preview bots (e.g., Slack-LinkExpanding, Slackbot, Slack-ImgProxy) will then issue outbound requests to the attacker-controlled URL, resulting in zero-click exfiltration of private data.

Affected

Anthropic · Slack MCP Server

CVSS v4.0 VULNCHECK

9.3 CRITICALCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:H/SI:H/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

EPSS

0.43% chance of exploitation in the next 30 days, 36th percentile

Published

2025-07-02

Proof-of-concept exploits (1)

• https://embracethered.com/blog/posts/2025/security-advisory-anthropic-slack-mcp-server-da…

References

• CVE Record
• NVD entry