CVE-2025-34072

Anthropic Slack MCP Server Data Exfiltration via Link Unfurling

CVSS 9.3 CRITICALEPSS 0.4%CWE-20 CWE-200

Vexday Risk Score

28Low

SSVC decision (CISA)

Track

No exploitation signal → monitor

CVSS 9.3EPSS 0.4%KEV nãoPoC —Nuclei —Metasploit —Patch —

Lifecycle

02 Jul 2025Published on NVD

Recommendation: Monitor — no exploitation signal at the moment.

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.

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:H/SI:H/SA:H

Affected products

Anthropic · Slack MCP Server

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References

https://embracethered.com/blog/posts/2025/security-advisory-anthropic-slack-mcp-server-data-leakage/https://vulncheck.com/advisories/anthropic-slack-mcp-server-data-exfiltration