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Description: Fix CVE-2017-14032: authentication bypass
If a malicious peer supplies an X.509 certificate chain that has more
than MBEDTLS_X509_MAX_INTERMEDIATE_CA intermediates (which by default is
8), it could bypass authentication of the certificates, when the
authentication mode was set to 'optional' eg.
MBEDTLS_SSL_VERIFY_OPTIONAL. The issue could be triggered remotely by
both the client and server sides.
.
Fix by backporting two patches from the upstream 2.6 branch:
d15795acd507 = Improve behaviour on fatal errors
31458a18788b = Only return VERIFY_FAILED from a single point
Author: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
Origin: backport, https://github.com/ARMmbed/mbedtls/commit/d15795acd5074e0b44e71f7ede8bdfe1b48591fc
Origin: backport, https://github.com/ARMmbed/mbedtls/commit/31458a18788b0cf0b722acda9bb2f2fe13a3fb32
Bug-Debian: https://bugs.debian.org/873557
---
This patch header follows DEP-3: http://dep.debian.net/deps/dep3/
--- a/library/x509_crt.c
+++ b/library/x509_crt.c
@@ -2055,8 +2055,8 @@ static int x509_crt_verify_child(
/* path_cnt is 0 for the first intermediate CA */
if( 1 + path_cnt > MBEDTLS_X509_MAX_INTERMEDIATE_CA )
{
- *flags |= MBEDTLS_X509_BADCERT_NOT_TRUSTED;
- return( MBEDTLS_ERR_X509_CERT_VERIFY_FAILED );
+ /* return immediately as the goal is to avoid unbounded recursion */
+ return( MBEDTLS_ERR_X509_FATAL_ERROR );
}
if( mbedtls_x509_time_is_past( &child->valid_to ) )
@@ -2200,11 +2200,14 @@ int mbedtls_x509_crt_verify_with_profile
mbedtls_x509_sequence *cur = NULL;
mbedtls_pk_type_t pk_type;
- if( profile == NULL )
- return( MBEDTLS_ERR_X509_BAD_INPUT_DATA );
-
*flags = 0;
+ if( profile == NULL )
+ {
+ ret = MBEDTLS_ERR_X509_BAD_INPUT_DATA;
+ goto exit;
+ }
+
if( cn != NULL )
{
name = &crt->subject;
@@ -2278,7 +2281,7 @@ int mbedtls_x509_crt_verify_with_profile
ret = x509_crt_verify_top( crt, parent, ca_crl, profile,
pathlen, selfsigned, flags, f_vrfy, p_vrfy );
if( ret != 0 )
- return( ret );
+ goto exit;
}
else
{
@@ -2293,17 +2296,28 @@ int mbedtls_x509_crt_verify_with_profile
ret = x509_crt_verify_child( crt, parent, trust_ca, ca_crl, profile,
pathlen, selfsigned, flags, f_vrfy, p_vrfy );
if( ret != 0 )
- return( ret );
+ goto exit;
}
else
{
ret = x509_crt_verify_top( crt, trust_ca, ca_crl, profile,
pathlen, selfsigned, flags, f_vrfy, p_vrfy );
if( ret != 0 )
- return( ret );
+ goto exit;
}
}
+exit:
+ /* prevent misuse of the vrfy callback */
+ if( ret == MBEDTLS_ERR_X509_CERT_VERIFY_FAILED )
+ ret = MBEDTLS_ERR_X509_FATAL_ERROR;
+
+ if( ret != 0 )
+ {
+ *flags = (uint32_t) -1;
+ return( ret );
+ }
+
if( *flags != 0 )
return( MBEDTLS_ERR_X509_CERT_VERIFY_FAILED );
--- a/include/mbedtls/error.h
+++ b/include/mbedtls/error.h
@@ -71,7 +71,7 @@
* Name ID Nr of Errors
* PEM 1 9
* PKCS#12 1 4 (Started from top)
- * X509 2 19
+ * X509 2 20
* PKCS5 2 4 (Started from top)
* DHM 3 9
* PK 3 14 (Started from top)
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -1042,7 +1042,7 @@ void mbedtls_ssl_conf_authmode( mbedtls_
*
* If set, the verify callback is called for each
* certificate in the chain. For implementation
- * information, please see \c x509parse_verify()
+ * information, please see \c mbedtls_x509_crt_verify()
*
* \param conf SSL configuration
* \param f_vrfy verification function
--- a/include/mbedtls/x509.h
+++ b/include/mbedtls/x509.h
@@ -76,6 +76,7 @@
#define MBEDTLS_ERR_X509_ALLOC_FAILED -0x2880 /**< Allocation of memory failed. */
#define MBEDTLS_ERR_X509_FILE_IO_ERROR -0x2900 /**< Read/write of file failed. */
#define MBEDTLS_ERR_X509_BUFFER_TOO_SMALL -0x2980 /**< Destination buffer is too small. */
+#define MBEDTLS_ERR_X509_FATAL_ERROR -0x3000 /**< A fatal error occured, eg the chain is too long or the vrfy callback failed. */
/* \} name */
/**
--- a/include/mbedtls/x509_crt.h
+++ b/include/mbedtls/x509_crt.h
@@ -267,7 +267,13 @@ int mbedtls_x509_crt_verify_info( char *
*
* All flags left after returning from the callback
* are also returned to the application. The function should
- * return 0 for anything but a fatal error.
+ * return 0 for anything (including invalid certificates)
+ * other than fatal error, as a non-zero return code
+ * immediately aborts the verification process. For fatal
+ * errors, a specific error code should be used (different
+ * from MBEDTLS_ERR_X509_CERT_VERIFY_FAILED which should not
+ * be returned at this point), or MBEDTLS_ERR_X509_FATAL_ERROR
+ * can be used if no better code is available.
*
* \note In case verification failed, the results can be displayed
* using \c mbedtls_x509_crt_verify_info()
--- a/library/error.c
+++ b/library/error.c
@@ -480,6 +480,8 @@ void mbedtls_strerror( int ret, char *bu
mbedtls_snprintf( buf, buflen, "X509 - Read/write of file failed" );
if( use_ret == -(MBEDTLS_ERR_X509_BUFFER_TOO_SMALL) )
mbedtls_snprintf( buf, buflen, "X509 - Destination buffer is too small" );
+ if( use_ret == -(MBEDTLS_ERR_X509_FATAL_ERROR) )
+ mbedtls_snprintf( buf, buflen, "X509 - A fatal error occured, eg the chain is too long or the vrfy callback failed" );
#endif /* MBEDTLS_X509_USE_C || MBEDTLS_X509_CREATE_C */
// END generated code
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