Vulnerability · Published Mar 10, 2026 · Assigned by GitHub_M

CVE-2026-26309Envoy has an off-by-one write in JsonEscaper::escapeString()

Medium 5.3

In plain English

A medium-severity security flaw in envoy from envoyproxy. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 36% of all known vulnerabilities).

Severity (CVSS 3.1)5.3Medium

Exploit odds (30 days)0.4%top 64.0% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

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 packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Go	github.com/envoyproxy/envoy	no fix listed	GHSA-56cj-wgg3-x943
Go	github.com/envoyproxy/envoy	no fix listed	GHSA-56cj-wgg3-x943
Go	github.com/envoyproxy/envoy	no fix listed	GHSA-56cj-wgg3-x943
Go	github.com/envoyproxy/envoy	no fix listed	GHSA-56cj-wgg3-x943

Affected products (as reported)

Vendor	Product	Versions
envoyproxy	envoy	>= 1.37.0, < 1.37.1>= 1.36.0, < 1.36.5>= 1.35.0, < 1.35.9< 1.34.13

Weakness: CWE-193 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

References

https://github.com/envoyproxy/envoy/security/advisories/GHSA-56cj-wgg3-x943 x_refsource_CONFIRM