CVE-2026-47778: Envoy improper certificate validation via NUL byte truncation in DNS SAN

CVE-2026-47778 · Severity: medium · CVSS 4.4 · Published 2026-06-26

Envoy is a popular open-source tool used to manage and secure network traffic between cloud applications. A flaw in how it checks security certificates allows an attacker to impersonate a trusted service by using a specially crafted certificate containing a hidden 'null' character. If successful, an attacker could intercept sensitive data or bypass security controls intended to verify the identity of backend servers.

Technologies: Envoy Proxy Envoy. Vendors: Envoy Proxy.

Quick answers

Is CVE-2026-47778 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-47778 being exploited in the wild.
How severe is CVE-2026-47778?
Medium severity, with a CVSS score of 4.4, published 26 June 2026.
Which products and versions are affected?
Envoy Proxy Envoy < 1.35.11, 1.36.0 to < 1.36.7, 1.37.0 to < 1.37.3, 1.38.0 to < 1.38.1.
Is there a fix for CVE-2026-47778?
No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-47778 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-47778?
Check whether you run Envoy Proxy Envoy at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

A vulnerability exists in Envoy's DefaultCertValidator::verifySubjectAltName due to improper handling of NUL bytes in DNS Subject Alternative Names (SANs). When extracting a DNS SAN, the string is cast to a C-style string using .c_str() before being passed to Utility::dnsNameMatch(). Because the underlying conversion to absl::string_view relies on strlen(), the string is prematurely truncated at the NUL byte. An attacker with a certificate containing a SAN like 'target.com\0.attacker.com' can successfully match against a required 'target.com' configuration. This allows an attacker who can obtain such a certificate from a trusted CA to perform Man-in-the-Middle (MITM) attacks against upstream routing. The issue is fixed by removing the .c_str() cast to ensure the full string length is preserved during comparison.

Affected products

  • Envoy Proxy Envoy < 1.35.11, 1.36.0 to < 1.36.7, 1.37.0 to < 1.37.3, 1.38.0 to < 1.38.1

Timeline

  • 2026-06-23: advisory: GitHub advisory GHSA-f8x4-rw5x-f3r7 published
  • 2026-06-26: disclosed: CVE-2026-47778 published to NVD

References

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