mTLS identity impersonation via null-truncated OTHERNAME SAN
Published Dec 3, 2025 · Updated Dec 3, 2025
Improper null termination in Envoy 1.36.2 and earlier allows remote authenticated users to impersonate an allowed mTLS identity. BMPSTRING and UNIVERSALSTRING OTHERNAME SAN values are converted to UTF-8, but assignment truncates the result at the first embedded null byte, so an exact matcher accepts only the attacker-controlled prefix. Exploitation requires a trusted client certificate carrying the crafted SAN and grants access to services or APIs protected by that exact identity check.
Summary
What happened
Improper null termination in Envoy 1.36.2 and earlier allows remote authenticated users to impersonate an allowed mTLS identity. BMPSTRING and UNIVERSALSTRING OTHERNAME SAN values are converted to UTF-8, but assignment truncates the result at the first embedded null byte, so an exact matcher accepts only the attacker-controlled prefix. Exploitation requires a trusted client certificate carrying the crafted SAN and grants access to services or APIs protected by that exact identity check.
The record
- CVE
- CVE-2025-66220
- Published
- Dec 3, 2025
- Updated
- Dec 3, 2025
- Vendor
- Envoy Proxy
- Product
- Envoy
- Classifications
- CWE-170, T1190
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Dec 3, 2025CVE publishedPublication date reported by the CVE source.
- Dec 3, 2025Record 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.
- Affected versionversion=<= 1.33.12
- Affected versionversion=>= 1.34.0, <= 1.34.10
- Affected versionversion=>= 1.35.0, <= 1.35.6
- Affected versionversion=>= 1.36.0, <= 1.36.2
What conditions does exploitation require?
What is affected?
Published CVSS scores
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.
Public exploit references
- Envoy embedded-null OTHERNAME SAN proof of conceptproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
See the directory against your own environment.
Your stack
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