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CVE-2026-26309— Envoy has an off-by-one write in JsonEscaper::escapeString()

Quick assessment

Affected
envoyproxy envoy
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Envoy是Enphase开源的一款用于连接智能家居设备的网关程序。 Envoy 1.37.1之前版本、1.36.5之前版本、1.35.8之前版本和1.34.13之前版本存在安全漏洞，该漏洞源于JsonEscaper::escapeString函数存在差一写入，可能导致崩溃或越界读取。

CVSS 5.3 · Medium EPSS 0.41% · P34

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application
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I. Basic Information for CVE-2026-26309

Vulnerability Information
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Vulnerability Title
Envoy has an off-by-one write in JsonEscaper::escapeString()
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Source: CVE Program / CVE List V5
Vulnerability Type
Off-by-one错误
Source: CVE Program / CVE List V5
Vulnerability Title
Envoy 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Envoy是Enphase开源的一款用于连接智能家居设备的网关程序。 Envoy 1.37.1之前版本、1.36.5之前版本、1.35.8之前版本和1.34.13之前版本存在安全漏洞，该漏洞源于JsonEscaper::escapeString函数存在差一写入，可能导致崩溃或越界读取。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
envoyproxy envoy >= 1.37.0, < 1.37.1 -

II. Public POCs for CVE-2026-26309

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III. Intelligence Information for CVE-2026-26309

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Vendor Advisories for CVE-2026-26309 (1)

Same Patch Batch · envoyproxy · 2026-03-10 · 5 CVEs total

CVE-2026-26308 7.5 HIGH Envoy has an RBAC Header Validation Bypass via Multi-Value Header Concatenation
CVE-2026-26310 5.9 MEDIUM Crash for scoped ip address in Envoy during DNS
CVE-2026-26311 5.9 MEDIUM Envoy HTTP: filter chain execution on reset streams causing UAF crash
CVE-2026-26330 5.3 MEDIUM Envoy global rate limit may crash when the response phase limit is enabled and the respons

IV. Related Vulnerabilities

Same product: envoy
Same vendor: envoyproxy
Same weakness: CWE-193

V. Comments for CVE-2026-26309

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