CVE-2026-26309: Envoyproxy Envoy

Medium severity, CVSS 5.3. EPSS: 0.4% chance of exploitation in the next 30 days.

Envoy is a high-performance edge/middle/service proxy. Prior to 1.37.1, 1.36.5, 1.35.8, and 1.34.13, an off-by-one write in Envoy::JsonEscaper::escapeString() can corrupt std::string null-termination, causing undefined behavior and potentially leading to crashes or out-of-bounds reads when the resulting string is later treated as a C-string. This vulnerability is fixed in 1.37.1, 1.36.5, 1.35.8, and 1.34.13.

Affected products

• Envoyproxy Envoy: before 1.34.13 (fixed in 1.34.13); from 1.35.0, before 1.35.8 (fixed in 1.35.8); from 1.36.0, before 1.36.5 (fixed in 1.36.5); version 1.37.0 only

Published 2026-03-10. Last modified 2026-06-17.