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Vulnerabilities

Vulnerability · CVE-2026-40396

Varnish Cache 9 before 9.0.1 allows a "workspace overflow" denial of service (daemon panic) after timeout_linger.

Published Apr 12, 2026 · catalog updated Jun 17, 2026 · vinyl cache

Check if you run it

No confirmed exploitation is on record for CVE-2026-40396. EPSS is 0.45%. Act only if a listed version of vinyl cache is installed.

Gaps on this record

  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
High7.5
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.45%
Remediation
Not established
Affected products
cpe vinyl-cache/vinyl cache

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 emerged from a port of the Varnish Enterprise non-blocking architecture for HTTP/2. New code was needed to adapt to a more recent workspace API that formalizes the pipelining operation. In addition to the workspace change on the Varnish Cache side, other differences created merge conflicts, like partial support for trailers in Varnish Enterprise. The conflict resolution missed one code path configuring pipelining to perform a complete workspace rollback, losing the guarantee that prefetched data would fit inside workspace_client during the transition from one request to the next. This can result in a workspace overflow, triggering a panic and crashing the Varnish server.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe vinyl-cache/vinyl cache9.0.0

How to fix CVE-2026-40396

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-40396. EPSS is 0.45%. Act only if a listed version of vinyl cache is installed.

Which versions are affected?

Compare what you have installed with vinyl-cache/vinyl cache 9.0.0. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-670: Always-Incorrect Control Flow Implementation. EPSS 0.45%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Apr 12, 2026 · NIST NVD

    Detected

    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

  2. Jun 17, 2026 · NIST NVD

    Updated

    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

Sources

  • CVE.orgVulnerability recordCVE-2026-40396

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-40396

    30-day exploitation probability 0.5%

    first.org
  • NIST NVDVulnerability recordCVE-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_linger) and resume traffic before the session

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.