What is CVE-2026-40396?

CVE-2026-40396 is a medium-severity vulnerability in Varnish-software Varnish Cache, classified under Always-Incorrect Control Flow Implementation. CVSS score: 4.0/10. Published 2026-04-12.

How severe is CVE-2026-40396?

Medium severity. CVSS v3 base score is 4.0 out of 10.

Vulnerability in Varnish-software Varnish Cache

CVE-2026-40396

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 long enough until the session releases its worker thread (timeout_linge…

EPSS: 0.000 (4.4th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 4.0 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:L.

Affected products

Varnish-software Varnish Cache — versions 9.0.0

Weakness classification (CWE)

CWE-670 — Always-Incorrect Control Flow Implementation

References

github.com/varnish/varnish/releases/tag/varnish-9.0.1
github.com/varnish/varnish/issues/15

Frequently asked questions

What is CVE-2026-40396?: CVE-2026-40396 is a medium-severity vulnerability in Varnish-software Varnish Cache, classified under Always-Incorrect Control Flow Implementation. CVSS score: 4.0/10. Published 2026-04-12.
How severe is CVE-2026-40396?: Medium severity. CVSS v3 base score is 4.0 out of 10.