CVE-2026-40396

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Summary

CVECVE-2026-40396
StatePUBLISHED
Assignermitre
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-04-12 20:16:19 UTC
Updated2026-04-13 15:01:43 UTC
DescriptionVarnish 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.

Risk And Classification

Primary CVSS: v3.1 4 MEDIUM from [email protected]

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:L

EPSS: 0.000120000 probability, percentile 0.016300000 (date 2026-04-14)

Problem Types: CWE-670 | CWE-670 CWE-670 Always-Incorrect Control Flow Implementation

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary4MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:L
3.1CNACVSS4MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:L

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Changed
Confidentiality
None
Integrity
None
Availability
Low

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:L

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Varnish-software Varnish Cache affected 9.0.0 9.0.1 semver Not specified

References

ReferenceSourceLinkTags
github.com/varnish/varnish/releases/tag/varnish-9.0.1 [email protected] github.com
github.com/varnish/varnish/issues/15 [email protected] github.com
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