CVE-2026-47778Public exploitNetwork attack vector

Host authentication bypass via NUL-truncated DNS SAN

Published Jun 26, 2026 · Updated Jun 26, 2026

Improper certificate validation in Envoy allows man-in-the-middle attackers to impersonate configured upstream TLS hosts. DefaultCertValidator::verifySubjectAltName passes a DNS SAN through c_str(), so dnsNameMatch uses strlen() and compares only the prefix before an embedded NUL. Exploitation requires auto_sni and auto_san_validation, a trusted CA that issues the malformed certificate, and upstream traffic interception; other SAN types are unaffected.

CVSS severity4.4
Medium
EPSS probability0.21%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper certificate validation in Envoy allows man-in-the-middle attackers to impersonate configured upstream TLS hosts. DefaultCertValidator::verifySubjectAltName passes a DNS SAN through c_str(), so dnsNameMatch uses strlen() and compares only the prefix before an embedded NUL. Exploitation requires auto_sni and auto_san_validation, a trusted CA that issues the malformed certificate, and upstream traffic interception; other SAN types are unaffected.

The record

CVE
CVE-2026-47778
Published
Jun 26, 2026
Updated
Jun 26, 2026
Vendor
Envoy Proxy
Product
Envoy
Classifications
CWE-158, T1557
Attack vector
network
Privileges
Unavailable

Timeline

How it unfolded

  1. Jun 26, 2026CVE publishedPublication date reported by the CVE source.
  2. Jun 26, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 1.35.11
  2. Affected versionversion=>= 1.36.0, < 1.36.7
  3. Affected versionversion=>= 1.37.0, < 1.37.3
  4. Affected versionversion=>= 1.38.0, < 1.38.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesUnavailable in this record.

What is affected?

Envoy Proxy · Envoyversion=< 1.35.11; version=>= 1.36.0, < 1.36.7; version=>= 1.37.0, < 1.37.3; version=>= 1.38.0, < 1.38.1

Published CVSS scores

4.4GitHub, Inc.CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-158Improper Neutralization of Null Byte or NUL Character
T1557Adversary-in-the-Middle

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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