What’s Vulnerable › Vulnerabilities

CVE-2025-34072: Anthropic Slack MCP Server Data Exfiltration via Link Unfurling

• Severity: critical (CVSS 9.3 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-07-02 · updated 2026-06-17
• Weakness: CWE-20

Description

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 products

• Anthropic Slack MCP Server: 0

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

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