CVE-2026-40395: Varnish Enterprise before 6.0.16r12 allows a "workspace overflow" denial of service (daemon panic) for shared

Q: How do I fix CVE-2026-40395?

varnish enterprise: upgrade to newer than 6.0.15. Exact commands for each OS are on this page.

Q: Is CVE-2026-40395 being exploited?

CVE-2026-40395 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-40395 affect?

CVE-2026-40395 affects varnish enterprise. Severity is medium (CVSS 4.0). Varnish Enterprise before 6.0.16r12 allows a "workspace overflow" denial of service (daemon panic) for shared VCL. The headerplus.write_req0() function from vmod_headerplus updates the underlying req0, which is normally the original read-on

Q: How urgent is CVE-2026-40395?

Priority 23/100. Remotely exploitable, no login, no user action

Routine

MEDIUM 4.0REMOTEUPGRADE

CVE-2026-40395 is a medium-severity flaw (CVSS 4.0) affecting varnish enterprise. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Varnish Enterprise before 6.0.16r12 allows a "workspace overflow" denial of service (daemon panic) for shared VCL. The headerplus.write_req0() function from vmod_headerplus updates the underlying req0, which is normally the original read-only request from which req is derived (readable and writable from VCL). This is useful in the active VCL, after amending req, to prepare a refined req0 before switching to a different VCL with the return (vcl(<l

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	4.0 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.2% (top 85%)
CISA exploited list	No
Weakness	CWE-770
Published	2026-04-12
Last modified	2026-10-26

Publisher (CNA): MITRE · Vendor: varnish-software

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 22:10 UTCUpdated Record last modified

varnish-software varnish enterprise UPGRADE

Affected: <= 6.0.15 · 6.0.16 r1 · 6.0.16 r10 · 6.0.16 r11 · 6.0.16 r2 · 6.0.16 r3 · 6.0.16 r4 · 6.0.16 r5

Fixed in: newer than 6.0.15

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy varnish-enterprise || rpm -q varnish-enterprise || varnish-enterprise --version

2. UPGRADE to newer than 6.0.15 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade varnish-enterprise

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade varnish-enterprise

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

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-2026-40395?

varnish enterprise: upgrade to newer than 6.0.15. Exact commands for each OS are on this page.

Is CVE-2026-40395 being exploited?

CVE-2026-40395 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-2026-40395 affect?

CVE-2026-40395 affects varnish enterprise. Severity is medium (CVSS 4.0). Varnish Enterprise before 6.0.16r12 allows a "workspace overflow" denial of service (daemon panic) for shared VCL. The headerplus.write_req0() function from vmod_headerplus updates the underlying req0, which is normally the original read-on

How urgent is CVE-2026-40395?

Priority 23/100. Remotely exploitable, no login, no user action

Software pages

Varnish vulnerabilities

Related CVEs

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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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