What is the CVSS score of CVE-2026-26309?

CVE-2026-26309 has a CVSS 3.1 base score of 5.3 (Medium). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L. EPSS exploitation probability: 0.0%.

Which versions of Envoy are affected by CVE-2026-26309?

Organizations using Envoy should be aware of moderate risk from CVE-2026-26309 rated CVSS 5.3. Exploitation could compromise the security of affected deployments.

Is there a public PoC exploit available for CVE-2026-26309?

Yes, a public proof-of-concept exploit is available for CVE-2026-26309. Prioritise patching immediately. EPSS: 0.0%.

How to fix or mitigate CVE-2026-26309?

Within 30 days: Identify affected systems and apply vendor patches as part of regular patch cycle. Monitor vendor channels for patch availability.

Envoy CVE-2026-26309

MEDIUM

Off-by-one Error (CWE-193)

2026-03-10 security-advisories@github.com

GHSA-56cj-wgg3-x943

Denial Of Service Envoy Envoyproxy

5.3

CVSS 3.1 · GitHub Advisory

Severity by source

GitHub Advisory PRIMARY

5.3 MEDIUM

AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Primary rating from GitHub Advisory · only source for this CVE.

CVSS VectorGitHub Advisory

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

Low

Lifecycle Timeline

Analysis Generated

Mar 12, 2026 - 21:55 vuln.today

PoC Detected

Mar 11, 2026 - 16:14 vuln.today

Public exploit code

CVE Published

Mar 10, 2026 - 20:16 nvd

MEDIUM 5.3

DescriptionGitHub Advisory

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.

AnalysisAI

Envoy is a high-performance edge/middle/service proxy. [CVSS 5.3 MEDIUM]

Technical ContextAI

Affects Envoy. 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.