CVE-2026-40396
What it is
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.
At a glance
- Exploitability
- Can be exploited over the network without logging in. Limited direct impact.
- Exploit odds
- 0.4% chance of exploitation in the next 30 days (EPSS).
- Fix
- A patch, advisory or fixed version is referenced. Upgrade or apply it.
Timeline
- PublishedDisclosed publicly on CVE.org and NVD
- Last updatedMost recent change to the record
Why it ranks here
- Exploited in the wild: no, CISA does not list it.
- Exploit odds: 0.4% in the next 30 days (EPSS).
- Severity: 4.0 MEDIUM (CVSS).
- Fix: a patch or advisory is linked.
Details
- Published
- Last modified
- Exploit probability
- 0.4% · EPSS, next 30 days
- Weakness
- CWE-670
- Record status
- Analyzed
Affected
- vinyl-cache Vinyl Cache 9.0.0
Attack profile CVSS 3.1 · 4.0
- Attack vector
- Network
- Complexity
- High
- Privileges needed
- None
- User interaction
- None
- Scope
- Changed
- Confidentiality
- None
- Integrity
- None
- Availability
- Low
Raw vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:L
Is it in your code?
Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.
Read https://cve-list.com/agent/cve/CVE-2026-40396.md and follow it. Check whether this project is affected by CVE-2026-40396. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.
