CVE-2026-47778

Description

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.

CVSS v3.1 Score

4.4

MEDIUM

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

EPSS — Exploit Prediction

0.0021

Probability of exploitation

0.12%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-158 CWE-158

Affected Products

Vendor	Product	Versions
envoyproxy	envoy	< 1.35.13
envoyproxy	envoy	1.36.0 — 1.36.9
envoyproxy	envoy	1.37.0 — 1.37.5
envoyproxy	envoy	1.38.0 — 1.38.3

References

Advisories & Patches

https://github.com/envoyproxy/envoy/security/advisories/GHSA-f8x4-rw5x-f3r7 https://github.com/envoyproxy/envoy/security/advisories/GHSA-f8x4-rw5x-f3r7

Exploits

https://github.com/envoyproxy/envoy/security/advisories/GHSA-f8x4-rw5x-f3r7 https://github.com/envoyproxy/envoy/security/advisories/GHSA-f8x4-rw5x-f3r7

Frequently Asked Questions

What is CVE-2026-47778? +

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. It has a CVSS v3.1 base score of 4.4 (MEDIUM).

How severe is CVE-2026-47778? +

CVE-2026-47778 has a CVSS v3.1 score of 4.4 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0021, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-47778? +

CVE-2026-47778 affects products from envoyproxy, specifically: envoy. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-47778? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

Related Vulnerabilities

CVE-2025-9648

A vulnerability in the CivetWeb library's function mg_handle_form_request allows remote attackers to trigger a denial of service (DoS) condition. By …

CVE-2025-47812 10.0

In Wing FTP Server before 7.4.4. the user and admin web interfaces mishandle '\0' bytes, ultimately allowing injection of arbitrary …

CVE-2025-14388 9.8

The PhastPress plugin for WordPress is vulnerable to Unauthenticated Arbitrary File Read via null byte injection in all versions up …

CVE-2025-55113 9.0

If the Access Control List is enforced by the Control-M/Agent and the C router is in use (default in Out-of-support …

CVE-2025-66263 7.5

Unauthenticated Arbitrary File Read via Null Byte Injection in DB Electronica Telecomunicazioni S.p.A. Mozart FM Transmitter versions 30, 50, 100, …

CVE-2025-1936 7.3

jar: URLs retrieve local file content packaged in a ZIP archive. The null and everything after it was ignored when …