SB2026040259 - Cache poisoning in Varnish Cache and Varnish Enterprise
Published: April 2, 2026
Security Bulletin ID
SB2026040259
Severity
Medium
Patch available
YES
Number of vulnerabilities
1
Exploitation vector
Remote access
Highest impact
Data manipulation
Breakdown by Severity
- Low
- Medium
- High
- Critical
Description
This security bulletin contains information about 1 security vulnerability.
1) Input validation error (CVE-ID: N/A)
The vulnerability allows a remote attacker to poison the cache or bypass authentication.
The vulnerability exists due to improper input validation in HTTP/1.1 request parsing when processing absolute form URIs. A remote attacker can send a specially crafted request with an absolute URL pointing to a root path (e.g., https://example.com/) to poison the cache or bypass authentication.
The attack is limited to root URLs with a path of /; deeper paths are not vulnerable.
Remediation
Install update from vendor's website.