PT-2026-32185 · Varnish · Varnish Cache

Published 2026-04-12 · Updated 2026-04-13 · CVE-2026-40396

Positive Technologies (AI Summary)

CVSS v3.1

7.5

High

Base vector

AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Name of the Vulnerable Software and Affected Versions Varnish Cache versions prior to 9.0.1

Description Varnish Cache 9 before 9.0.1 is susceptible to a denial of service due to a workspace overflow, potentially leading to a daemon panic. A malicious client can exploit this by sending an HTTP/1 request, waiting for the session to release its worker thread, and then resuming traffic before the session is fully closed, sending multiple requests simultaneously. This triggers a pipelining operation that can cause a workspace overflow, resulting in a server crash. The issue stems from a port of the Varnish Enterprise non-blocking architecture for HTTP/2 and incomplete workspace rollback during pipelining configuration.

Recommendations Update to Varnish Cache version 9.0.1 or later.

Fix

DoS

Weakness Enumeration

CWE-670

Related Identifiers

CVE-2026-40396

Affected Products

Varnish Cache

References · 9

• https://osv.dev/vulnerability/UBUNTU-CVE-2026-40396 · Vendor Advisory
• https://nvd.nist.gov/vuln/detail/CVE-2026-40396 · Security Note
• https://ubuntu.com/security/CVE-2026-40396 · Vendor Advisory
• https://cve.org/CVERecord?id=CVE-2026-40396 · Security Note
• https://github.com/varnish/varnish/issues/15 · Note
• https://github.com/varnish/varnish/releases/tag/varnish-9.0.1 · Note
• https://docs.varnish-software.com/security/VEV00002 · Note
• https://twitter.com/CVEnew/status/2043561040500150691 · Twitter Post
• https://twitter.com/VulmonFeeds/status/2043430072384635353 · Twitter Post