CVE-2026-40394
MediumCVSS 4.0Exploitation Probability (EPSS)
Low risk15th percentile - higher than 15% of all known CVEs
Summary
Varnish Cache 9 before 9.0.1 and Varnish Enterprise before 6.0.16r11 allow a "workspace overflow" denial of service (daemon panic) for certain amounts of prefetched data. During HTTP/2 upgrade, a buffer allocation splits the workspace, and the next fetch may run out of workspace.
Risk Assessment
A malicious client could crash the Varnish server, causing service unavailability.
Recommendation
Update Varnish Cache to version 9.0.1 or later and Varnish Enterprise to version 6.0.16r11 or later.
Other vulnerabilities in Varnish Cache
See all- CVE-2026-50052Low
In Vinyl Cache before 9.0.1 and Varnish Cache before 9.0.3, a deficiency in HTTP/2 request parsing can be exploited for backend request desync (request smuggling), leading to cache poisoning, authentication bypass, or information disclosure. The attack only works if HTTP/2 is enabled (disabled by default).
- CVE-2026-40396Medium
Varnish Cache 9 before 9.0.1 allows a "workspace overflow" denial of service (daemon panic) after timeout_linger. A malicious client could send an HTTP/1 request, wait until the session releases its worker thread (timeout_linger), and resume traffic before the session is closed (timeout_idle) by sending more than one request at once to trigger pipelining and workspace overflow. The vulnerability stems from a porting error of the non-blocking architecture from Varnish Enterprise.
- CVE-2026-34475Medium
Varnish Cache before 8.0.1 and Varnish Enterprise before 6.0.16r12, in certain unchecked req.url scenarios, mishandle URLs with a path of / for HTTP/1.1. This may lead to cache poisoning or authentication bypass.
Original NVD description (English source)
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS