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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 16:05:55 +01:00
parent 9f1320ff0c
commit c4824c8f38
1 changed files with 68 additions and 7 deletions
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71
src/drv_imap.c
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@ -48,6 +48,7 @@
# include <openssl/ssl.h> # include <openssl/ssl.h>
# include <openssl/err.h> # include <openssl/err.h>
# include <openssl/hmac.h> # include <openssl/hmac.h>
# include <openssl/x509v3.h>
#endif #endif
typedef struct imap_server_conf { typedef struct imap_server_conf {
@ -187,9 +188,65 @@ static const char *Flags[] = {
#if HAVE_LIBSSL #if HAVE_LIBSSL
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 ))) {
fprintf( stderr, "Error, cannot get certificate subject\n" );
return -1;
}
if ((len = X509_NAME_get_text_by_NID( subj, NID_commonName, cname, sizeof(cname) )) < 0) {
fprintf( stderr, "Error, cannot get certificate common name\n" );
return -1;
}
if (strlen( cname ) == (size_t)len && host_matches( hostname, cname ))
return 0;
fprintf( stderr, "Error, certificate owner does not match hostname %s\n", hostname );
return -1;
}
/* this gets called when a certificate is to be verified */ /* this gets called when a certificate is to be verified */
static int static int
verify_cert( SSL *ssl ) verify_cert( SSL *ssl, const char *hostname )
{ {
X509 *cert; X509 *cert;
int err; int err;
@ -204,12 +261,16 @@ verify_cert( SSL *ssl )
} }
err = SSL_get_verify_result( ssl ); err = SSL_get_verify_result( ssl );
if (err == X509_V_OK) if (err != X509_V_OK) {
return 0;
fprintf( stderr, "Error, can't verify certificate: %s (%d)\n", fprintf( stderr, "Error, can't verify certificate: %s (%d)\n",
X509_verify_cert_error_string(err), err ); X509_verify_cert_error_string(err), err );
goto intcheck;
}
if (hostname && verify_hostname( cert, hostname ) < 0)
goto intcheck;
return 0;
intcheck:
X509_NAME_oneline( X509_get_subject_name( cert ), buf, sizeof(buf) ); X509_NAME_oneline( X509_get_subject_name( cert ), buf, sizeof(buf) );
info( "\nSubject: %s\n", buf ); info( "\nSubject: %s\n", buf );
X509_NAME_oneline( X509_get_issuer_name( cert ), buf, sizeof(buf) ); X509_NAME_oneline( X509_get_issuer_name( cert ), buf, sizeof(buf) );
@ -1103,7 +1164,7 @@ start_tls( imap_store_t *ctx )
} }
/* verify the server certificate */ /* verify the server certificate */
if (verify_cert( imap->buf.sock.ssl )) if (verify_cert( imap->buf.sock.ssl, ((imap_store_conf_t *)ctx->gen.conf)->server->host ))
return 1; return 1;
imap->buf.sock.use_ssl = 1; imap->buf.sock.use_ssl = 1;