SB2026040259 - Cache poisoning in Varnish Cache and Varnish Enterprise

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Main Vulnerability Database SB2026040259

SB2026040259 - Cache poisoning in Varnish Cache and Varnish Enterprise

Published: April 2, 2026

Security Bulletin ID SB2026040259
CSH Severity
Medium
Patch available
YES
Number of vulnerabilities 1
Exploitation vector Remote access
Highest impact Data manipulation

Breakdown by Severity

Medium 100%
  • Low
  • Medium
  • High
  • Critical

Description

This security bulletin contains information about 1 vulnerability.


1) Input validation error (CVE-ID: N/A)

CWE-ID: CWE-20 - Improper input validation

CVSSv4: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Green


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.

References