EUVD-2026-21738CVSS Vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:L
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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.
Analysis
Denial of service via workspace overflow in Varnish Cache 9 before 9.0.1 and Varnish Enterprise before 6.0.16r11 allows unauthenticated remote attackers to trigger daemon panic through HTTP/2 session upgrade with specific amounts of prefetched data. The vulnerability exploits improper buffer allocation during HTTP/1 to HTTP/2 transport upgrade, causing workspace exhaustion on subsequent pipelined fetch operations. …
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