What is CVE-2026-26309?

CVE-2026-26309 is a medium-severity vulnerability in Envoyproxy Envoy, classified under Off-by-one Error. CVSS score: 5.3/10. Published 2026-03-10.

How severe is CVE-2026-26309?

Medium severity. CVSS v3 base score is 5.3 out of 10.

Vulnerability in Envoyproxy Envoy

CVE-2026-26309

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 potenti…

EPSS: 0.000 (0.2th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L.

Affected products

Envoyproxy Envoy — versions >= 1.37.0, < 1.37.1, >= 1.36.0, < 1.36.5, >= 1.35.0, < 1.35.9

Weakness classification (CWE)

CWE-193 — Off-by-one Error

References

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

Frequently asked questions

What is CVE-2026-26309?: CVE-2026-26309 is a medium-severity vulnerability in Envoyproxy Envoy, classified under Off-by-one Error. CVSS score: 5.3/10. Published 2026-03-10.
How severe is CVE-2026-26309?: Medium severity. CVSS v3 base score is 5.3 out of 10.