CVE-2025-34072

Anthropic Slack MCP Server Data Exfiltration via Link Unfurling

Severity Score

9.3

*CVSS v4

Exploit Likelihood

*EPSS

Affected Versions

*CPE

Public Exploits

*Multiple Sources

Exploited in Wild

*KEV

Decision

Track*

*SSVC

Descriptions

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.

*Credits: wunderwuzzi of Embrace The Red

CVSS Scores

Attack Vector

Network

Attack Complexity

Low

Attack Requirements

None

Privileges Required

None

User Interaction

None

System

Vulnerable | Subsequent

Confidentiality

High

Integrity

None

High

Availability

None

High

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

None

Availability

None

Attack Vector

Network

Attack Complexity

Medium

Authentication

None

Confidentiality

Partial

Integrity

None

Availability

None

* Common Vulnerability Scoring System

SSVC

Decision:Track*

Exploitation

Poc

Automatable

Tech. Impact

Partial

* Organization's Worst-case Scenario

Timeline

2025-04-15 CVE Reserved
2025-07-02 CVE Published
2025-07-02 CVE Updated
2025-07-02 First Exploit
---------- EPSS Updated
---------- Exploited in Wild
---------- KEV Due Date

CWE

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

CAPEC

CAPEC-34: HTTP Response Splitting

References (2)

URL	Tag	Source
https://vulncheck.com/advisories/anthropic-slack-mcp-server-data-exfiltration	Third Party Advisory

URL	Date	SRC
https://embracethered.com/blog/posts/2025/security-advisory-anthropic-slack-mcp-server-data-leakage	2025-07-02

URL	Date	SRC

URL	Date	SRC

Affected Vendors, Products, and Versions

Vendor		Product				Version		Other		Status
Vendor	Product	Version	Other	Status	<-- -->	Vendor	Product	Version	Other	Status
Anthropic Search vendor "Anthropic"		Slack MCP Server Search vendor "Anthropic" for product "Slack MCP Server"				0 Search vendor "Anthropic" for product "Slack MCP Server" and version "0"		en		Affected