Medium severity · published Mar 10, 2026
CVE-2026-26309
Envoy has an off-by-one write in JsonEscaper::escapeString()
5.3
CVSS
0.4%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
Low
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.4% · higher than 33% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
EN
envoy · envoyproxy
>= 1.37.0, < 1.37.1; >= 1.36.0, < 1.36.5; >= 1.35.0, < 1.35.9; < 1.34.13 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-26309
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-26309
Exploit
https://github.com/envoyproxy/envoy/security/advisories/GHSA-56cj-wgg3-x943
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