https://vinyl-cache.org/security/VSV00019.html says: Originally published 2026-05-18, last updated 2026-06-28

CVE-2026-50052

A deficiency in HTTP/2 request parsing can be exploited to launch a backend request desync attack (request smuggling), which in turn can be used for cache poisoning, authentication bypass or possibly even information disclosure and manipulation.

The attack vector only exists if HTTP/2 support is enabled by setting the feature parameter to contain +http2. HTTP/2 support is disabled by default.

We recommend to upgrade to a version which is not affected, to disable HTTP/2 support or to mitigate the issue in VCL, as detailed below.

Versions affected

- Vinyl Cache 9.0.0

- Varnish Cache by Varnish Software up to and including 9.0.2

- All Varnish Cache Releases from 7.6.0 up to and including 8.0.1

- Varnish Cache 6.0 LTS series from 6.0.14 up to and including 6.0.17.

Versions not affected

- Vinyl Cache 9.0.1 (released 2026-05-18)

- Vinyl Cache main branch at commit dfc27fb4e7bf110945f5c145ce95b8de14ead77f or later

- Varnish Cache by Varnish Software 9.0.3 (released 2026-05-18)

- Varnish Cache 8.0.2 (released 2026-05-18)

- Varnish Cache 6.0 LTS version 6.0.18 (2026-05-18)

- Varnish Enterprise by Varnish Software

Mitigation Options

Several options to mitigate this issue exist. The safest is disabling HTTP/2. [See https://vinyl-cache.org/security/VSV00019.html for full details.] Acknowledgements and credits

We thank Lam Jun Rong of Calif.io, who used Anthropic Research’s tool “Claude”, for reporting this issue.

For the Vinyl Cache project, the issue has been handled by Nils Goroll of UPLEX. The merged fix is a slight variation of the proposed fix by Lam Jun Rong, which had already been found independently by Dridi Boukelmoune. https://blog.calif.io/p/mad-bugs-my-cousin-vinyl-cve-2026 provides the story of how it was found by the researcher.