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GHSA-rwjg-c3h2-f57p
No affected components available
Summary
Envoy’s mTLS certificate matcher for match_typed_subject_alt_names may incorrectly treat certificates containing an embedded null byte (\0) inside an OTHERNAME SAN value as valid matches.
Details
This occurs when the SAN is encoded as a BMPSTRING or UNIVERSALSTRING, and its UTF-8 conversion result is truncated at the first null byte during string assignment. As a result, "victim\0evil" may match an exact: "victim" rule and be accepted by Envoy.
PoC
Create a CA and a server certificate signed by that CA. Create two client certificates signed by the same CA: client_evil with OTHERNAME BMPSTRING = "evil" client_null with OTHERNAME BMPSTRING = "victim\0evil" Configure Envoy with require_client_certificate: true and a match_typed_subject_alt_names entry for the OTHERNAME OID with matcher.exact: "victim". Connect without a client cert → connection rejected. Connect with client_evil → connection rejected. Connect with client_null → connection accepted (but shouldn't!).
Impact
An attacker who can obtain a trusted client certificate with a null byte embedded in an OTHERNAME SAN can exploit this vulnerability. The practical impact is unauthorized impersonation of the matched identity, enabling access to services or APIs protected by that exact OTHERNAME check.
Credit
The vulnerability can be exploited over the network without needing physical access. It is difficult for an attacker to exploit this vulnerability and may require special conditions. An attacker needs high-level or administrative privileges. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a high impact on the confidentiality of the information. There is a low impact on the integrity of the data.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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