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%.

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

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Vulnerability Assessment

Weakness	CWE CWE-193 OWASP Top 10:2025 A06:2021 - Vulnerable and Outdated Components ASVS 5.0 V15 - Secure Coding and Architecture Off-by-one prevention
Impact	CVSS 5.3 (MEDIUM). Attack vector: Network. Complexity: Low. Privileges required: None. User interaction: None. Public exploit/POC available.
Exploit ScenarioDerived	An attacker could exploit this flaw, crashes or out-of-bounds reads when the resulting string is.

This Month Plan within 30 days. Why: MEDIUM severity (CVSS 4.0-6.9).

No patch listed yet 0.0% exploitation probability (EPSS)

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AnalysisAIv1 – Mar 12, 2026

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

RemediationAI

Fixed in version 1.37.1. Restrict network access to the affected service where possible.

Affected Packages

go github.com/envoyproxy/envoy no fix

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 1 package in go

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

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.

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Exploit and PoC references, threat intelligence from 22 sources

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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

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.

Executive ViewAI

Why It Matters

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. Proof-of-concept code is publicly available. Organizations should apply vendor updates when available and monitor for exploitation.

Business Impact: Low

Compensating Controls

Apply vendor patch. If patching is delayed: restrict network access and enable monitoring.

Threat Intelligence Overview

EPSS Score

0.0%

Top 100% exploitable

Exploit

POC

Public exploit code exists

Data Quality

5 sources

Confidence: Medium

NVD

CVE.org

EPSS

GitHub

VulDB

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue

Severity MEDIUM

CISA KEV No

Public POC Yes

EPSS 0.0%

Patch available No

Active threat No

Deciding rule

MEDIUM severity (CVSS 4.0-6.9)

What every action level means

Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.

Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.

This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.

This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.

Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived

Scheduled

Exploitation· derived

Poc

System Exposure· derived

Open

Automatable· derived

Yes

Human Impact

Low

Priority Score

Low Medium High Critical

KEV: 0

EPSS: 0

CVSS: +26

PoC: +20

Weaponized: 0

Threat intel: 0

Gov advisory: 0

Attack Technique

Denial of Service MEDIUM

Denial of Service attacks render applications or systems unavailable by overwhelming resources or triggering failure conditions.

Affected Products (CPE)GitHub Advisory

cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:*

cpe:2.3:a:envoyproxy:envoy:1.37.0:*:*:*:*:*:*:*

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References

Advisories & patches

ADVISORY https://vuldb.com/?id.350182

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