Envoy: Embedded NUL in TLS DNS SAN Truncation in the Default TLS Certificate Validator. (Auth Bypass)

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Summary

CVECVE-2026-47778
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-06-26 18:16:59 UTC
Updated2026-06-26 19:50:17 UTC
DescriptionEnvoy is an open source edge and service proxy designed for cloud-native applications. Prior to 1.35.11, 1.36.7, 1.37.3, and 1.38.1, a structural flaw was identified in DefaultCertValidator::verifySubjectAltName where the extracted DNS SAN string is cast to a C-style string using .c_str() before being passed to the Utility::dnsNameMatch() algorithm. If the attacker serves a certificate with a dNSName SAN containing an embedded NUL byte, the helper Utility::generalNameAsString captures the complete string including the NUL. However, when .c_str() evaluates it, implicit conversion to absl::string_view inside dnsNameMatch relies on strlen(), prematurely truncating the evaluation context. Envoy evaluates trucated string against the exact required config_san match and returns true, thereby successfully validating the string with the Nul byte for an upstream routing. This vulnerability is fixed in 1.35.11, 1.36.7, 1.37.3, and 1.38.1.

Risk And Classification

Primary CVSS: v3.1 4.4 MEDIUM from [email protected]

CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:N/A:N

Problem Types: CWE-158 | CWE-158 CWE-158: Improper Neutralization of Null Byte or NUL Character

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary4.4MEDIUMCVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:N/A:N
3.1CNADECLARED4.4MEDIUMCVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:N/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
High
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:N/A:N

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Envoyproxy Envoy affected >= 1.38.0, < 1.38.1 Not specified
CNA Envoyproxy Envoy affected >= 1.37.0, < 1.37.3 Not specified
CNA Envoyproxy Envoy affected >= 1.36.0, < 1.36.7 Not specified
CNA Envoyproxy Envoy affected < 1.35.11 Not specified

References

ReferenceSourceLinkTags
github.com/envoyproxy/envoy/security/advisories/GHSA-f8x4-rw5x-f3r7 [email protected] github.com
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