Buffer overflow in Varnish Cache - #VU150675
Published: September 17, 2026
Vulnerability identifier: #VU150675
CSH Severity: Medium
CVSS v4: 8.2 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
CVE-ID: N/A
CWE-ID: CWE-120
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to cause a denial of service.
The vulnerability exists due to a workspace buffer overflow in the .upper() and .lower() VCL string type methods when processing a crafted request containing a string that exhausts the remaining workspace. A remote attacker can send a specially crafted request to cause a denial of service.
Exploitation requires prior knowledge of the VCL in use and a string that fills the remaining workspace while staying within request size limits.
Affected software
Varnish Cache
Remediation
Install security update from vendor's website.
Varnish Cache - update to 9.0.4