CVE-2026-40394 | Varnish Cache up to 9.0.0 control flow

VDB-357045 · CVE-2026-40394 · GCVE-0-2026-40394 VARNISH CACHE UP TO 9.0.0 CONTROL FLOW HISTORYDIFFRELATEJSONXMLCTI CVSS Meta Temp Score Current Exploit Price (≈) CTI Interest Score 3.8 $0-$5k 0.57 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. Productinfo Name Varnish Cache Version 9.0 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 Vector Complexity Authentication Confidentiality Integrity Availability Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock 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 Price Prediction: 🔍 Current Price Estimation: 🔒 0-Day Unlock Unlock Unlock Unlock Today Unlock Unlock Unlock Unlock 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: 99:953:101 Discussion No comments yet. Languages: en. Please log in to comment. ◂ PreviousOverviewNext ▸