CVE-2026-40396: Varnish Cache 9 before 9.0.1 allows a "workspace overflow" denial of service (daemon panic) after timeout_ling

Routine

MEDIUM 4.0REMOTEDOWNGRADE

CVE-2026-40396 is a medium-severity flaw (CVSS 4.0) affecting vinyl cache. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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_linger) and resume traffic before the session is closed (timeout_idle) sending more than one request at once to trigger a pipelining operation between requests. This vulnerability affecting Varnish Cache 9.0.0 emerge

Why this priority

Remotely exploitable, no login, no user action

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	4.0 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 72%)
CISA exploited list	No
Weakness	CWE-670
Published	2026-04-12
Last modified	2026-10-26

Publisher (CNA): MITRE · Vendor: vinyl-cache

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-12 20:16 UTCPublished CVE record published
2026-10-26 21:10 UTCUpdated Record last modified

vinyl-cache vinyl cache DOWNGRADE

Affected: 9.0.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 9.0.0

1. Check installed version

apt-cache policy vinyl-cache || rpm -q vinyl-cache || vinyl-cache --version

2. No fixed release: DOWNGRADE to a release before 9.0.0 (Debian / Ubuntu)

apt-cache madison vinyl-cache sudo apt install vinyl-cache=<VERSION_BEFORE_9.0.0> sudo apt-mark hold vinyl-cache

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list vinyl-cache sudo dnf downgrade vinyl-cache-<VERSION_BEFORE_9.0.0> sudo dnf versionlock add vinyl-cache

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-40396?

vinyl cache: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2026-40396 being exploited?

CVE-2026-40396 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-40396 affect?

CVE-2026-40396 affects vinyl cache. Severity is medium (CVSS 4.0). 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_linger

How urgent is CVE-2026-40396?

Priority 26/100. Remotely exploitable, no login, no user action

Software pages

Varnish vulnerabilities

Related CVEs

CVE-2026-34475 MEDIUM 5.4 UPGRADE UPGRADE Varnish Cache before 8.0.1 and Varnish Enterprise before 6.0.16r12, in certain unchecked req.url scenarios, mi
CVE-2026-40394 MEDIUM 4.0 UPGRADE DOWNGRADE Varnish Cache 9 before 9.0.1 and Varnish Enterprise before 6.0.16r11 allows a "workspace overflow" denial of s

References

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