CVE-2026-26309
Envoyproxy Envoy ≤ 1.34.13
Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:LSummary
CVE-2026-26309 is a medium-severity Off-by-one Error (CWE-193) vulnerability in Envoyproxy Envoy. Its CVSS base score is 5.3 (Medium).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 29th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SI-2 (Flaw Remediation) — see the control section below for these in your framework.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-10800
Vulnerability Data
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…
more
as a C-string. This vulnerability is fixed in 1.37.1, 1.36.5, 1.35.8, and 1.34.13.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Off-by-one memory corruption in public-facing Envoy proxy enables remote crashes/OOB reads via crafted input (T1190); maps to application exploitation for DoS impact (T1499.004).
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
Mitigating Controls (NIST 800-53 r5) AI
Directly requires applying the vendor patches (1.37.1+) that correct the off-by-one write in JsonEscaper::escapeString().
Mandates developer security testing and fuzzing that would detect the off-by-one error and resulting null-terminator corruption before release.
Provides memory-protection mechanisms that can contain or block exploitation of the undefined behavior and out-of-bounds reads caused by the corrupted std::string.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Secure SDLC practices directly prevent off-by-one errors via reviews, static analysis, and testing.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Security testing in development and acceptance can detect off-by-one errors before release.
Secure development life cycle includes requirements and reviews that can catch off-by-one errors.
Application security requirements can specify bounds-checking and input validation to prevent off-by-one errors.
Secure system architecture and engineering principles promote defensive coding practices that reduce off-by-one mistakes.
Secure coding directly addresses off-by-one errors through coding standards and peer review.