CVE-2023-35944: Envoyproxy Envoy

Medium severity, CVSS 5.3. EPSS: 0.7% chance of exploitation in the next 30 days.

Envoy is an open source edge and service proxy designed for cloud-native applications. Envoy allows mixed-case schemes in HTTP/2, however, some internal scheme checks are case-sensitive. Prior to versions 1.27.0, 1.26.4, 1.25.9, 1.24.10, and 1.23.12, this can lead to the rejection of requests with mixed-case schemes such as `htTp` or `htTps`, or the bypassing of some requests such as `https` in unencrypted connections. With a fix in versions 1.27.0, 1.26.4, 1.25.9, 1.24.10, and 1.23.12, Envoy will now lowercase scheme values by default, and change the internal scheme checks that were case-sensitive to be case-insensitive. There are no known workarounds for this issue.

Affected products

• Envoyproxy Envoy: from 1.23.0, before 1.23.12 (fixed in 1.23.12); from 1.24.0, before 1.24.10 (fixed in 1.24.10); from 1.25.0, before 1.25.9 (fixed in 1.25.9); from 1.26.0, before 1.26.4 (fixed in 1.26.4)

Published 2023-07-25. Last modified 2026-06-17.