What is the CVSS score of EUVD-2026-39818?

EUVD-2026-39818 has a CVSS 3.1 base score of 4.4 (Medium). CVSS vector: CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:N/A:N. EPSS exploitation probability: 0.2%.

Is there a patch available for EUVD-2026-39818?

Yes, a patch is available for EUVD-2026-39818. Update the affected software to the latest version immediately.

Envoy Proxy EUVD-2026-39818

| CVE-2026-47778 MEDIUM

Improper Neutralization of Null Byte or NUL Character (CWE-158)

2026-06-26 GitHub_M

Information Disclosure Envoy

4.4

CVSS 3.1 · Vendor: GitHub_M

Severity by source

Vendor (GitHub_M) PRIMARY

4.4 MEDIUM

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

vuln.today AI

5.9 MEDIUM

AV:N for network-delivered attack; AC:H for required upstream control or MITM position; PR:N because the attacker needs no privileges on the Envoy instance itself, only control of an external upstream endpoint.

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

4.0 AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Primary rating from Vendor (GitHub_M).

CVSS VectorVendor: GitHub_M

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

Attack Vector

Network

Attack Complexity

High

Privileges Required

High

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

None

Availability

None

Lifecycle Timeline

Patch available

Jun 26, 2026 - 19:02 EUVD

Analysis Generated

Jun 26, 2026 - 18:35 vuln.today

DescriptionCVE.org

Envoy 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.

AnalysisAI

Certificate SAN validation in Envoy Proxy is bypassed when an attacker-controlled upstream serves a TLS certificate containing an embedded NUL byte in the dNSName Subject Alternative Name field. Envoy versions prior to 1.35.11, 1.36.7, 1.37.3, and 1.38.1 are affected, allowing an attacker who controls or can impersonate an upstream TLS endpoint to pass Envoy's configured SAN match check with a fraudulent certificate and intercept proxied traffic. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Recon

Control or MITM upstream TLS endpoint

Delivery

Craft X.509 cert with NUL byte in dNSName SAN

Exploit

Present cert during Envoy upstream TLS handshake

Install

.c_str() causes strlen() truncation in dnsNameMatch

Truncated SAN matches configured config_san

Execute

Certificate validation returns true

Impact

Intercept or observe proxied upstream traffic

Recon

Control or MITM upstream TLS endpoint

Delivery

Craft X.509 cert with NUL byte in dNSName SAN

Exploit

Present cert during Envoy upstream TLS handshake

Install

.c_str() causes strlen() truncation in dnsNameMatch

Truncated SAN matches configured config_san

Execute

Certificate validation returns true

Impact

Intercept or observe proxied upstream traffic

Vulnerability AssessmentAI

Exploitation	Exploitation requires that the attacker be in a network position to serve a TLS certificate to Envoy acting as a TLS client connecting to an upstream - either by directly controlling the upstream server or by executing a man-in-the-middle attack on the Envoy-to-upstream network segment. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment	The vendor-provided CVSS 3.1 vector AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:N/A:N yields a score of 4.4, reflecting high attack complexity and a high privilege prerequisite. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario	An attacker who controls or can perform a man-in-the-middle attack against an upstream server that Envoy routes traffic to crafts a TLS certificate with a dNSName SAN of 'trusted.example.com\x00.attacker.com' and presents it during the TLS handshake. Envoy's verifySubjectAltName extracts the full SAN string but the subsequent .c_str() call causes strlen()-based truncation inside dnsNameMatch, reducing the evaluated string to 'trusted.example.com', which matches the operator-configured config_san. …
Remediation	The definitive fix is upgrading Envoy to a patched release: 1.35.11, 1.36.7, 1.37.3, or 1.38.1, per the vendor GitHub Security Advisory at https://github.com/envoyproxy/envoy/security/advisories/GHSA-f8x4-rw5x-f3r7. … Detailed patch versions, workarounds, and compensating controls in full report.