What’s Vulnerable › Vulnerabilities
CVE-2026-40394
- Severity: high (CVSS 7.5 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.2% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2026-04-12 · updated 2026-10-26
- Weakness: CWE-670
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.
Affected products
- varnish-software Varnish Enterprise: through 6.0.15; 6.0.16-r1, 6.0.16-r10, 6.0.16-r2, 6.0.16-r3, 6.0.16-r4, 6.0.16-r5 (+4)
- varnish-software Varnish Cache: 9.0.0
References
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