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 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.
Published · last modified .
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.
EPSS exploit prediction
EPSS: 0.004 (33.6th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 34th percentile — 33.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: +0.001
Affected products
- Envoyproxy Envoy — versions >= 1.37.0, < 1.37.1, 1.37.0, < 1.34.13
Weakness classification (CWE)
References
- github.com/envoyproxy/envoy/security/advisories/GHSA-56cj-wgg3-x943 (Exploit, Vendor Advisory)
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.