Vulnerability Description
Varnish Cache 9 before 9.0.1 and Varnish Enterprise before 6.0.16r11 allows a "workspace overflow" denial of service (daemon panic) for certain amounts of prefetched data. The setup of an HTTP/2 session starts with a speculative HTTP/1 transport, and upon upgrading to h2 the HTTP/1 request is repurposed as stream zero. During the upgrade, a buffer allocation is made to reserve space to send frames to the client. This allocation would split the original workspace, and depending on the amount of prefetched data, the next fetch could perform a pipelining operation that would run out of workspace.
CVSS Score
MEDIUM
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Varnish-Software | Varnish Enterprise | <= 6.0.15 |
| Vinyl-Cache | Vinyl Cache | 9.0.0 |
Related Weaknesses (CWE)
References
- https://docs.varnish-software.com/security/VEV00002/Vendor Advisory
FAQ
What is CVE-2026-40394?
CVE-2026-40394 is a vulnerability with a CVSS score of 4.0 (MEDIUM). Varnish Cache 9 before 9.0.1 and Varnish Enterprise before 6.0.16r11 allows a "workspace overflow" denial of service (daemon panic) for certain amounts of prefetched data. The setup of an HTTP/2 sessi...
How severe is CVE-2026-40394?
CVE-2026-40394 has been rated MEDIUM with a CVSS base score of 4.0/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-40394?
Check the references section above for vendor advisories and patch information. Affected products include: Varnish-Software Varnish Enterprise, Vinyl-Cache Vinyl Cache.