CVE-2025-30346
📋 TL;DR
This vulnerability allows attackers to perform client-side desync attacks via HTTP/1 requests against Varnish Cache and Varnish Enterprise. Attackers can poison caches and potentially bypass security controls by manipulating HTTP request sequences. Organizations using affected versions of Varnish as reverse proxies or caching servers are impacted.
💻 Affected Systems
- Varnish Cache
- Varnish Enterprise
📦 What is this software?
Varnish Cache by Varnish Cache Project
Varnish Enterprise by Varnish Software
Varnish Enterprise by Varnish Software
Varnish Enterprise by Varnish Software
Varnish Enterprise by Varnish Software
Varnish Enterprise by Varnish Software
Varnish Enterprise by Varnish Software
Varnish Enterprise by Varnish Software
Varnish Enterprise by Varnish Software
Varnish Enterprise by Varnish Software
Varnish Enterprise by Varnish Software
Varnish Enterprise by Varnish Software
Varnish Enterprise by Varnish Software
Varnish Enterprise by Varnish Software
Varnish Enterprise by Varnish Software
Varnish Enterprise by Varnish Software
Varnish Enterprise by Varnish Software
Varnish Enterprise by Varnish Software
Varnish Enterprise by Varnish Software
Varnish Enterprise by Varnish Software
Varnish Enterprise by Varnish Software
Varnish Enterprise by Varnish Software
Varnish Enterprise by Varnish Software
Varnish Enterprise by Varnish Software
Varnish Enterprise by Varnish Software
Varnish Enterprise by Varnish Software
⚠️ Risk & Real-World Impact
Worst Case
Cache poisoning leading to credential theft, malware distribution, or complete bypass of security controls like WAFs and authentication mechanisms.
Likely Case
Cache poisoning resulting in defacement, injection of malicious content, or bypass of specific security rules.
If Mitigated
Limited impact due to proper request validation, but potential for cache manipulation still exists.
🎯 Exploit Status
Exploitation requires crafting specific HTTP/1 request sequences but does not require authentication.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Varnish Cache 7.6.2+, Varnish Enterprise 6.0.13r10+
Vendor Advisory: https://varnish-cache.org/security/VSV00015.html
Restart Required: Yes
Instructions:
1. Download patched version from official repositories. 2. Stop Varnish service. 3. Install updated package. 4. Restart Varnish service. 5. Verify version with 'varnishd -V'.
🔧 Temporary Workarounds
HTTP/2 Enforcement
allForce clients to use HTTP/2 which is not vulnerable to this attack
Configure load balancer or frontend to require HTTP/2 connections
Request Validation
allImplement strict HTTP request validation at upstream servers
Configure web application firewalls to validate HTTP request sequences
🧯 If You Can't Patch
- Implement strict request validation and sanitization at upstream application servers
- Deploy WAF with HTTP request sequence validation capabilities
🔍 How to Verify
Check if Vulnerable:
Check Varnish version with 'varnishd -V' and compare against affected versionsCheck Version:
varnishd -VVerify Fix Applied:
Confirm version is 7.6.2+ for Varnish Cache or 6.0.13r10+ for Varnish Enterprise📡 Detection & Monitoring
Log Indicators:
- Unusual HTTP request sequences
- Multiple requests with same connection headers
- Cache poisoning patterns
Network Indicators:
- HTTP/1 requests with crafted connection headers
- Request smuggling attempts
SIEM Query:
source="varnish" AND (http_request_sequence="abnormal" OR connection_header="malformed")