dbcve.org
Improper Input ValidationWeakness · CWE-20

CVE-2025-34072

CRITICAL · 9.3 CVSS v4.0 Published 2025-07-02
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

This vulnerability affects Anthropic's deprecated Slack MCP Server. When an AI agent using this server processes untrusted data, malicious actors can manipulate it to generate messages containing hyperlinks that embed sensitive data. Slack's automatic link preview functionality (Slack-LinkExpanding, Slackbot, Slack-ImgProxy) then triggers outbound requests to attacker-controlled URLs, enabling zero-click exfiltration of confidential information.

MitigationImmediate action: discontinue use of the deprecated Slack MCP Server and migrate to supported alternatives. If continued use is unavoidable, disable automatic link unfurling in Slack workspace settings and implement strict input sanitization on all data processed by the MCP Server.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
Authentication
X
User interaction
None
Scope
X

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify if Slack MCP Server is installed
    List installed MCP servers or check application inventory for packages named 'slack-mcp', 'anthropic-slack-mcp', or similar. On Linux, check /opt, /usr/local/bin, or user-installed node_modules directories for slack-mcp related binaries or packages.
    Affected if The deprecated Slack MCP Server from Anthropic is present in the environment
  2. Determine the installed version of Slack MCP Server
    Run 'npm list slack-mcp' or 'pip show slack-mcp' if installed via pip, or check package.json if it's a Node.js project. Compare the version against the deprecated release known to contain this vulnerability.
    Affected if The version matches the deprecated/release known to be affected by CVE-2025-34072 (the specific vulnerable release)
  3. Verify if the server processes external or untrusted input
    Review configuration files (config.json, .env, or similar) for the MCP server. Check if the server accepts input from untrusted sources, external APIs, or user-provided prompts that could contain malicious content.
    Affected if The Slack MCP Server is configured to process untrusted or external data without sanitization
  4. Check Slack workspace link unfurling settings
    In Slack, navigate to Workspace Settings > Security & Permissions > Link Sharing, or visit workspace admin settings. Look for 'Enable automatic link unfurling' or 'Expand links in messages' options.
    Affected if Automatic link unfurling/preview is enabled in the Slack workspace settings

A user is affected if they are running the deprecated Anthropic Slack MCP Server (vulnerable version), it processes untrusted input, AND automatic link unfurling is enabled in their Slack workspace, allowing outbound requests to attacker-controlled URLs.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Immediate action: discontinue use of the deprecated Slack MCP Server and migrate to supported alternatives. If continued use is unavoidable, disable automatic link unfurling in Slack workspace settings and implement strict input sanitization on all data processed by the MCP Server.

Have this fixed Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA2.0 h
18.0 hours of engineering $3,200
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2025-34072 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
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