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Create configuration option to bypass the mbedtls_ssl_set_hostname check

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Update generated files.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2025-02-13 13:46:58 +01:00
parent 63f958df77
commit ae59c52322
7 changed files with 68 additions and 1 deletions
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40
include/mbedtls/config.h
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@ -1713,6 +1713,46 @@
*/
//#define MBEDTLS_SSL_ASYNC_PRIVATE
/** \def MBEDTLS_SSL_CLI_ALLOW_WEAK_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME
*
* In TLS clients, when a client authenticates a server through its
* certificate, the client normally checks three things:
* - the certificate chain must be valid;
* - the chain must start from a trusted CA;
* - the certificate must cover the server name that is expected by the client.
*
* Omitting any of these checks is generally insecure, and can allow a
* malicious server to impersonate a legitimate server.
*
* The third check may be safely skipped in some unusual scenarios,
* such as networks where eavesdropping is a risk but not active attacks,
* or a private PKI where the client equally trusts all servers that are
* accredited by the root CA.
*
* You should call mbedtls_ssl_set_hostname() with the expected server name
* before starting a TLS handshake on a client (unless the client is
* set up to only use PSK-based authentication, which does not rely on the
* host name). This configuration option controls what happens if a TLS client
* is configured with the authentication mode #MBEDTLS_SSL_VERIFY_REQUIRED
* (default), certificate authentication is enabled and the client does not
* call mbedtls_ssl_set_hostname():
*
* - If this option is unset (default), the connection attempt is aborted
* with the error #MBEDTLS_ERR_SSL_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME.
* - If this option is set, the TLS library does not check the server name
* that the certificate is valid for. This is the historical behavior
* of Mbed TLS, but may be insecure as explained above.
*
* Enable this option for strict backward compatibility if you have
* determined that it is secure in the scenario where you are using
* Mbed TLS.
*
* \deprecated This option exists only for backward compatibility and will
* be removed in the next major version of Mbed TLS.
*
*/
//#define MBEDTLS_SSL_CLI_ALLOW_WEAK_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME
/**
* \def MBEDTLS_SSL_CONTEXT_SERIALIZATION
*

3
include/mbedtls/ssl.h
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@ -213,6 +213,9 @@
* #MBEDTLS_SSL_VERIFY_REQUIRED (default).
* - Certificate authentication is enabled.
* - The client does not call mbedtls_ssl_set_hostname().
* - The configuration option
* #MBEDTLS_SSL_CLI_ALLOW_WEAK_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME
* is not enabled.
*/
#define MBEDTLS_ERR_SSL_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME -0x5D80

2
library/error.c
View File

@ -509,7 +509,7 @@ const char *mbedtls_high_level_strerr(int error_code)
case -(MBEDTLS_ERR_SSL_CACHE_ENTRY_NOT_FOUND):
return( "SSL - Cache entry not found" );
case -(MBEDTLS_ERR_SSL_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME):
return( "SSL - Attempt to verify a certificate without an expected hostname. This is usually insecure. In TLS clients, when a client authenticates a server through its certificate, the client normally checks three things: - the certificate chain must be valid; - the chain must start from a trusted CA; - the certificate must cover the server name that is expected by the client. Omitting any of these checks is generally insecure, and can allow a malicious server to impersonate a legitimate server. The third check may be safely skipped in some unusual scenarios, such as networks where eavesdropping is a risk but not active attacks, or a private PKI where the client equally trusts all servers that are accredited by the root CA. You should call mbedtls_ssl_set_hostname() with the expected server name before starting a TLS handshake on a client (unless the client is set up to only use PSK-based authentication, which does not rely on the host name). If you have determined that server name verification is not required for security in your scenario, call mbedtls_ssl_set_hostname() with \\p NULL as the server name. This error is raised if all of the following conditions are met: - A TLS client is configured with the authentication mode #MBEDTLS_SSL_VERIFY_REQUIRED (default). - Certificate authentication is enabled. - The client does not call mbedtls_ssl_set_hostname()" );
return( "SSL - Attempt to verify a certificate without an expected hostname. This is usually insecure. In TLS clients, when a client authenticates a server through its certificate, the client normally checks three things: - the certificate chain must be valid; - the chain must start from a trusted CA; - the certificate must cover the server name that is expected by the client. Omitting any of these checks is generally insecure, and can allow a malicious server to impersonate a legitimate server. The third check may be safely skipped in some unusual scenarios, such as networks where eavesdropping is a risk but not active attacks, or a private PKI where the client equally trusts all servers that are accredited by the root CA. You should call mbedtls_ssl_set_hostname() with the expected server name before starting a TLS handshake on a client (unless the client is set up to only use PSK-based authentication, which does not rely on the host name). If you have determined that server name verification is not required for security in your scenario, call mbedtls_ssl_set_hostname() with \\p NULL as the server name. This error is raised if all of the following conditions are met: - A TLS client is configured with the authentication mode #MBEDTLS_SSL_VERIFY_REQUIRED (default). - Certificate authentication is enabled. - The client does not call mbedtls_ssl_set_hostname(). - The configuration option #MBEDTLS_SSL_CLI_ALLOW_WEAK_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME is not enabled" );
#endif /* MBEDTLS_SSL_TLS_C */
#if defined(MBEDTLS_X509_USE_C) || defined(MBEDTLS_X509_CREATE_C)

3
library/version_features.c
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@ -486,6 +486,9 @@ static const char * const features[] = {
#if defined(MBEDTLS_SSL_ASYNC_PRIVATE)
"MBEDTLS_SSL_ASYNC_PRIVATE",
#endif /* MBEDTLS_SSL_ASYNC_PRIVATE */
#if defined(MBEDTLS_SSL_CLI_ALLOW_WEAK_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME)
"MBEDTLS_SSL_CLI_ALLOW_WEAK_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME",
#endif /* MBEDTLS_SSL_CLI_ALLOW_WEAK_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME */
#if defined(MBEDTLS_SSL_CONTEXT_SERIALIZATION)
"MBEDTLS_SSL_CONTEXT_SERIALIZATION",
#endif /* MBEDTLS_SSL_CONTEXT_SERIALIZATION */

12
programs/test/query_config.c
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@ -1376,6 +1376,14 @@ int query_config(const char *config)
}
#endif /* MBEDTLS_SSL_ASYNC_PRIVATE */
#if defined(MBEDTLS_SSL_CLI_ALLOW_WEAK_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME)
if( strcmp( "MBEDTLS_SSL_CLI_ALLOW_WEAK_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME", config ) == 0 )
{
MACRO_EXPANSION_TO_STR( MBEDTLS_SSL_CLI_ALLOW_WEAK_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME );
return( 0 );
}
#endif /* MBEDTLS_SSL_CLI_ALLOW_WEAK_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME */
#if defined(MBEDTLS_SSL_CONTEXT_SERIALIZATION)
if( strcmp( "MBEDTLS_SSL_CONTEXT_SERIALIZATION", config ) == 0 )
{
@ -3506,6 +3514,10 @@ void list_config(void)
OUTPUT_MACRO_NAME_VALUE(MBEDTLS_SSL_ASYNC_PRIVATE);
#endif /* MBEDTLS_SSL_ASYNC_PRIVATE */
#if defined(MBEDTLS_SSL_CLI_ALLOW_WEAK_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME)
OUTPUT_MACRO_NAME_VALUE(MBEDTLS_SSL_CLI_ALLOW_WEAK_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME);
#endif /* MBEDTLS_SSL_CLI_ALLOW_WEAK_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME */
#if defined(MBEDTLS_SSL_CONTEXT_SERIALIZATION)
OUTPUT_MACRO_NAME_VALUE(MBEDTLS_SSL_CONTEXT_SERIALIZATION);
#endif /* MBEDTLS_SSL_CONTEXT_SERIALIZATION */

1
scripts/config.py
View File

@ -326,6 +326,7 @@ def crypto_adapter(adapter):
DEPRECATED = frozenset([
'MBEDTLS_SSL_PROTO_SSL3',
'MBEDTLS_SSL_CLI_ALLOW_WEAK_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME',
'MBEDTLS_SSL_SRV_SUPPORT_SSLV2_CLIENT_HELLO',
])

8
tests/suites/test_suite_config.mbedtls_boolean.data
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@ -1264,6 +1264,14 @@ Config: !MBEDTLS_SSL_CBC_RECORD_SPLITTING
depends_on:!MBEDTLS_SSL_CBC_RECORD_SPLITTING:MBEDTLS_SSL_CLI_C:MBEDTLS_SSL_SRV_C
pass:
Config: MBEDTLS_SSL_CLI_ALLOW_WEAK_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME
depends_on:MBEDTLS_SSL_CLI_ALLOW_WEAK_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME:MBEDTLS_SSL_CLI_C:MBEDTLS_SSL_SRV_C
pass:
Config: !MBEDTLS_SSL_CLI_ALLOW_WEAK_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME
depends_on:!MBEDTLS_SSL_CLI_ALLOW_WEAK_CERTIFICATE_VERIFICATION_WITHOUT_HOSTNAME:MBEDTLS_SSL_CLI_C:MBEDTLS_SSL_SRV_C
pass:
Config: MBEDTLS_SSL_CLI_C
depends_on:MBEDTLS_SSL_CLI_C
pass: