CVE-2025-34072

Anthropic Slack MCP Server Data Exfiltration via Link Unfurling

State: Published
Severity: 9.3 Critical
Published: Jul 2, 2025
Updated: Jul 2, 2025
Reserved: Apr 15, 2025

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.

Scores

CVSS	Score	Vector	Source
4.0	9.3 Critical	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	VulnCheck

Weaknesses

CWE-200 Exposure of Sensitive Information to an Unauthorized Actor
CWE-20 Improper Input Validation

Affected Products

Product	Versions
Slack MCP ServerAnthropic	0Affected

References

https://embracethered.com/blog/posts/2025/security-advisory-anthropic-slack-mcp-server-data-leakage/third-party-advisorytechnical-descriptionexploit
https://vulncheck.com/advisories/anthropic-slack-mcp-server-data-exfiltrationthird-party-advisory

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