Vulnerability · Published Jul 2, 2025 · Assigned by VulnCheck

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

Critical 9.3

In plain English

A critical-severity information exposure in Slack MCP Server from Anthropic. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 37% of all known vulnerabilities).

Severity (CVSS 4.0)9.3Critical

Exploit odds (30 days)0.4%top 62.6% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official 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 (as reported)

Vendor	Product	Versions
Anthropic	Slack MCP Server	0

Weakness: CWE-200, CWE-20 · Vector: 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

References

https://embracethered.com/blog/posts/2025/security-advisory-anthropic-slack-mcp-server-data-leakage/ third-party-advisory, technical-description, exploit
https://vulncheck.com/advisories/anthropic-slack-mcp-server-data-exfiltration third-party-advisory