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fix CVE-2013-0289: add SSL subject verification

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we did not check a valid certificate's subject at all so far.
this is no problem if the certificate file contains only exactly the
wanted host's certificate - before revision 04fdf7d1 (dec 2000, < v0.4),
this was even enforced (more or less - if the peer cert had been
signed directly by a root cert, it would be accepted as well).
however, when the file contains root certificates (like the system-wide
certificate file typically does), any host with a valid certificate
could pretend to be the wanted host.
This commit is contained in:
Oswald Buddenhagen 2013-02-03 17:34:15 +01:00
parent fbba8f1cda
commit 8310cf78ac
1 changed files with 69 additions and 5 deletions
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74
src/socket.c
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@ -28,6 +28,7 @@
# include <openssl/ssl.h>
# include <openssl/err.h>
# include <openssl/hmac.h>
# include <openssl/x509v3.h>
#endif
#include "isync.h"
@ -118,6 +119,62 @@ compare_certificates( X509 *cert, X509 *peercert,
return 0;
}
static int
host_matches( const char *host, const char *pattern )
{
if (pattern[0] == '*' && pattern[1] == '.') {
pattern += 2;
if (!(host = strchr( host, '.' )))
return 0;
host++;
}
return *host && *pattern && !strcasecmp( host, pattern );
}
static int
verify_hostname( X509 *cert, const char *hostname )
{
int i, len, found;
X509_NAME *subj;
STACK_OF(GENERAL_NAME) *subj_alt_names;
char cname[1000];
/* try the DNS subjectAltNames */
found = 0;
if ((subj_alt_names = X509_get_ext_d2i( cert, NID_subject_alt_name, NULL, NULL ))) {
int num_subj_alt_names = sk_GENERAL_NAME_num( subj_alt_names );
for (i = 0; i < num_subj_alt_names; i++) {
GENERAL_NAME *subj_alt_name = sk_GENERAL_NAME_value( subj_alt_names, i );
if (subj_alt_name->type == GEN_DNS &&
strlen( (const char *)subj_alt_name->d.ia5->data ) == (size_t)subj_alt_name->d.ia5->length &&
host_matches( hostname, (const char *)(subj_alt_name->d.ia5->data) ))
{
found = 1;
break;
}
}
sk_GENERAL_NAME_pop_free( subj_alt_names, GENERAL_NAME_free );
}
if (found)
return 0;
/* try the common name */
if (!(subj = X509_get_subject_name( cert ))) {
error( "Error, cannot get certificate subject\n" );
return -1;
}
if ((len = X509_NAME_get_text_by_NID( subj, NID_commonName, cname, sizeof(cname) )) < 0) {
error( "Error, cannot get certificate common name\n" );
return -1;
}
if (strlen( cname ) == (size_t)len && host_matches( hostname, cname ))
return 0;
error( "Error, certificate owner does not match hostname %s\n", hostname );
return -1;
}
#if OPENSSL_VERSION_NUMBER >= 0x00904000L
#define READ_X509_KEY(fp, key) PEM_read_X509( fp, key, 0, 0 )
#else
@ -146,6 +203,8 @@ verify_cert( const server_conf_t *conf, conn_t *sock )
}
while (conf->cert_file) { /* while() instead of if() so break works */
/* Note: this code intentionally does no hostname verification. */
if (X509_cmp_current_time( X509_get_notBefore( cert )) >= 0) {
error( "Server certificate is not yet valid\n" );
break;
@ -164,7 +223,7 @@ verify_cert( const server_conf_t *conf, conn_t *sock )
}
err = -1;
for (lcert = 0; READ_X509_KEY( fp, &lcert ); )
if (!(err = compare_certificates( lcert, cert, md, n )))
if (!(err = compare_certificates( lcert, cert, md, n ))) /* TODO: check X509v3 [Extended] Key Usage? */
break;
X509_free( lcert );
fclose( fp );
@ -193,11 +252,16 @@ verify_cert( const server_conf_t *conf, conn_t *sock )
X509_STORE_CTX_init( &xsc, mconf->cert_store, cert, 0 );
err = X509_verify_cert( &xsc ) > 0 ? 0 : X509_STORE_CTX_get_error( &xsc );
X509_STORE_CTX_cleanup( &xsc );
if (!err)
return 0;
error( "Error, cannot verify certificate: %s (%d)\n",
X509_verify_cert_error_string( err ), err );
if (err) {
error( "Error, cannot verify certificate: %s (%d)\n",
X509_verify_cert_error_string( err ), err );
goto intcheck;
}
if (conf->host && verify_hostname( cert, conf->host ) < 0)
goto intcheck;
return 0;
intcheck:
X509_NAME_oneline( X509_get_subject_name( cert ), buf, sizeof(buf) );
info( "\nSubject: %s\n", buf );
X509_NAME_oneline( X509_get_issuer_name( cert ), buf, sizeof(buf) );