Improper Validation of Certificate with Host Mismatch

The product communicates with a host that provides a certificate, but the product does not properly ensure that the certificate is actually associated with that host.


Even if a certificate is well-formed, signed, and follows the chain of trust, it may simply be a valid certificate for a different site than the site that the product is interacting with. If the certificate's host-specific data is not properly checked - such as the Common Name (CN) in the Subject or the Subject Alternative Name (SAN) extension of an X.509 certificate - it may be possible for a redirection or spoofing attack to allow a malicious host with a valid certificate to provide data, impersonating a trusted host. In order to ensure data integrity, the certificate must be valid and it must pertain to the site that is being accessed.

Even if the product attempts to check the hostname, it is still possible to incorrectly check the hostname. For example, attackers could create a certificate with a name that begins with a trusted name followed by a NUL byte, which could cause some string-based comparisons to only examine the portion that contains the trusted name.

This weakness can occur even when the product uses Certificate Pinning, if the product does not verify the hostname at the time a certificate is pinned.


The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

The following OpenSSL code obtains a certificate and verifies it.

cert = SSL_get_peer_certificate(ssl);
if (cert && (SSL_get_verify_result(ssl)==X509_V_OK)) {

  // do secret things


Even though the "verify" step returns X509_V_OK, this step does not include checking the Common Name against the name of the host. That is, there is no guarantee that the certificate is for the desired host. The SSL connection could have been established with a malicious host that provided a valid certificate.

See Also

Comprehensive Categorization: Access Control

Weaknesses in this category are related to access control.

OWASP Top Ten 2021 Category A07:2021 - Identification and Authentication Failures

Weaknesses in this category are related to the A07 category "Identification and Authentication Failures" in the OWASP Top Ten 2021.

Identify Actors

Weaknesses in this category are related to the design and architecture of a system's identification management components. Frequently these deal with verifying that ex...

Comprehensive CWE Dictionary

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Weaknesses in Mobile Applications

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