CVE-2025-34072CWE-20CWE-200

Anthropic Slack MCP Server Data Exfiltration via Link Unfurling

Critical · published July 2, 2025

CVSS v4.0
9.3
EPSS
0%
Percentile
36.2
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v4.0
9.3 · CRITICAL
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
EPSS
0.00430 · 36.2th percentile
Weaknesses
CWE-20 · Improper Input Validation; CWE-200 · Exposure of Sensitive Information to an Unauthorized Actor
Published
2025-07-02T13:46Z
EPSS history
Timeline
  • 02 JUL 13:46Z
    Anthropic Slack MCP Server Data Exfiltration via Link Unfurling
    cvelistv5