Varnish Cache up to 9.0.0 control flow

CVSS Meta Temp Score
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Current Exploit Price (≈)
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CTI Interest Score
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3.8$0-$5k0.19

Summaryinfo

A vulnerability has been found in Varnish Cache up to 9.0.0 and classified as problematic. The impacted element is an unknown function. Performing a manipulation results in control flow. This vulnerability is known as CVE-2026-40394. Remote exploitation of the attack is possible. No exploit is available. The affected component should be upgraded.

Detailsinfo

A vulnerability was found in Varnish Cache up to 9.0.0. It has been classified as problematic. This affects an unknown part. The manipulation with an unknown input leads to a control flow vulnerability. CWE is classifying the issue as CWE-670. The code contains a control flow path that does not reflect the algorithm that the path is intended to implement, leading to incorrect behavior any time this path is navigated. This is going to have an impact on availability. The summary by CVE is:

Varnish Cache 9 before 9.0.1 and Varnish Enterprise before 6.0.16r11 allows a "workspace overflow" denial of service (daemon panic) for certain amounts of prefetched data. The setup of an HTTP/2 session starts with a speculative HTTP/1 transport, and upon upgrading to h2 the HTTP/1 request is repurposed as stream zero. During the upgrade, a buffer allocation is made to reserve space to send frames to the client. This allocation would split the original workspace, and depending on the amount of prefetched data, the next fetch could perform a pipelining operation that would run out of workspace.

The advisory is shared at docs.varnish-software.com. This vulnerability is uniquely identified as CVE-2026-40394 since 04/12/2026. The exploitability is told to be difficult. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. Neither technical details nor an exploit are publicly available.

Upgrading to version 9.0.1 eliminates this vulnerability.

If you want to get the best quality for vulnerability data then you always have to consider VulDB.

Productinfo

Name

Version

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 3.8
VulDB Meta Temp Score: 3.8

VulDB Base Score: 3.7
VulDB Temp Score: 3.6
VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA Base Score: 4.0
CNA Vector (MITRE): 🔒

CVSSv2info

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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Control flow
CWE: CWE-670
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Varnish Cache 9.0.1

Timelineinfo

04/12/2026 Advisory disclosed
04/12/2026 +0 days CVE reserved
04/12/2026 +0 days VulDB entry created
04/12/2026 +0 days VulDB entry last update

Sourcesinfo

Advisory: docs.varnish-software.com
Status: Confirmed

CVE: CVE-2026-40394 (🔒)
GCVE (CVE): GCVE-0-2026-40394
GCVE (VulDB): GCVE-100-357045

Entryinfo

Created: 04/12/2026 22:20
Changes: 04/12/2026 22:20 (61)
Complete: 🔍
Cache ID: 216:F9F:103

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