Fix various certificate fingerprint issues.

By using non-DER or invalid encodings outside the signed portion of a
certificate the fingerprint can be changed without breaking the signature.
Although no details of the signed portion of the certificate can be changed
this can cause problems with some applications: e.g. those using the
certificate fingerprint for blacklists.

1. Reject signatures with non zero unused bits.

If the BIT STRING containing the signature has non zero unused bits reject
the signature. All current signature algorithms require zero unused bits.

2. Check certificate algorithm consistency.

Check the AlgorithmIdentifier inside TBS matches the one in the
certificate signature. NB: this will result in signature failure
errors for some broken certificates.

3. Check DSA/ECDSA signatures use DER.

Reencode DSA/ECDSA signatures and compare with the original received
signature. Return an error if there is a mismatch.

This will reject various cases including garbage after signature
(thanks to Antti Karjalainen and Tuomo Untinen from the Codenomicon CROSS
program for discovering this case) and use of BER or invalid ASN.1 INTEGERs
(negative or with leading zeroes).

CVE-2014-8275
Reviewed-by: Emilia Käsper <emilia@openssl.org>

CHANGES

@@ -659,6 +659,43 @@
 
  Changes between 1.0.1j and 1.0.1k [xx XXX xxxx]
 
+  *) Fix various certificate fingerprint issues.
+
+     By using non-DER or invalid encodings outside the signed portion of a
+     certificate the fingerprint can be changed without breaking the signature.
+     Although no details of the signed portion of the certificate can be changed
+     this can cause problems with some applications: e.g. those using the
+     certificate fingerprint for blacklists.
+
+     1. Reject signatures with non zero unused bits.
+
+     If the BIT STRING containing the signature has non zero unused bits reject
+     the signature. All current signature algorithms require zero unused bits.
+
+     2. Check certificate algorithm consistency.
+
+     Check the AlgorithmIdentifier inside TBS matches the one in the
+     certificate signature. NB: this will result in signature failure
+     errors for some broken certificates.
+
+     Thanks to Konrad Kraszewski from Google for reporting this issue.
+
+     3. Check DSA/ECDSA signatures use DER.
+
+     Reencode DSA/ECDSA signatures and compare with the original received
+     signature. Return an error if there is a mismatch.
+
+     This will reject various cases including garbage after signature
+     (thanks to Antti Karjalainen and Tuomo Untinen from the Codenomicon CROSS
+     program for discovering this case) and use of BER or invalid ASN.1 INTEGERs
+     (negative or with leading zeroes).
+
+     Further analysis was conducted and fixes were developed by Stephen Henson
+     of the OpenSSL core team.
+
+     (CVE-2014-8275)
+     [Steve Henson]
+
    *) Do not resume sessions on the server if the negotiated protocol
       version does not match the session's version. Resuming with a different
       version, while not strictly forbidden by the RFC, is of questionable

crypto/asn1/a_verify.c

@@ -90,6 +90,12 @@ int ASN1_verify(i2d_of_void *i2d, X509_ALGOR *a, ASN1_BIT_STRING *signature,
 		ASN1err(ASN1_F_ASN1_VERIFY,ASN1_R_UNKNOWN_MESSAGE_DIGEST_ALGORITHM);
 		goto err;
 		}
+
+	if (signature->type == V_ASN1_BIT_STRING && signature->flags & 0x7)
+		{
+		ASN1err(ASN1_F_ASN1_VERIFY, ASN1_R_INVALID_BIT_STRING_BITS_LEFT);
+		goto err;
+		}
 	
 	inl=i2d(data,NULL);
 	buf_in=OPENSSL_malloc((unsigned int)inl);
@@ -150,6 +156,12 @@ int ASN1_item_verify(const ASN1_ITEM *it, X509_ALGOR *a,
 		return -1;
 		}
 
+	if (signature->type == V_ASN1_BIT_STRING && signature->flags & 0x7)
+		{
+		ASN1err(ASN1_F_ASN1_VERIFY, ASN1_R_INVALID_BIT_STRING_BITS_LEFT);
+		return -1;
+		}
+
 	EVP_MD_CTX_init(&ctx);
 
 	/* Convert signature OID into digest and public key OIDs */

crypto/dsa/dsa_asn1.c

@@ -177,13 +177,25 @@ int DSA_verify(int type, const unsigned char *dgst, int dgst_len,
 	     const unsigned char *sigbuf, int siglen, DSA *dsa)
 	{
 	DSA_SIG *s;
+	const unsigned char *p = sigbuf;
+	unsigned char *der = NULL;
+	int derlen = -1;
 	int ret=-1;
 
 	s = DSA_SIG_new();
 	if (s == NULL) return(ret);
-	if (d2i_DSA_SIG(&s,&sigbuf,siglen) == NULL) goto err;
+	if (d2i_DSA_SIG(&s,&p,siglen) == NULL) goto err;
+	/* Ensure signature uses DER and doesn't have trailing garbage */
+	derlen = i2d_DSA_SIG(s, &der);
+	if (derlen != siglen || memcmp(sigbuf, der, derlen))
+		goto err;
 	ret=DSA_do_verify(dgst,dgst_len,s,dsa);
 err:
+	if (derlen > 0)
+		{
+		OPENSSL_cleanse(der, derlen);
+		OPENSSL_free(der);
+		}
 	DSA_SIG_free(s);
 	return(ret);
 	}

crypto/ecdsa/ecs_vrf.c

@@ -57,6 +57,7 @@
  */
 
 #include "ecs_locl.h"
+#include "cryptlib.h"
 #ifndef OPENSSL_NO_ENGINE
 #include <openssl/engine.h>
 #endif
@@ -86,13 +87,25 @@ int ECDSA_verify(int type, const unsigned char *dgst, int dgst_len,
 		const unsigned char *sigbuf, int sig_len, EC_KEY *eckey)
  	{
 	ECDSA_SIG *s;
+	const unsigned char *p = sigbuf;
+	unsigned char *der = NULL;
+	int derlen = -1;
 	int ret=-1;
 
 	s = ECDSA_SIG_new();
 	if (s == NULL) return(ret);
-	if (d2i_ECDSA_SIG(&s, &sigbuf, sig_len) == NULL) goto err;
+	if (d2i_ECDSA_SIG(&s, &p, sig_len) == NULL) goto err;
+	/* Ensure signature uses DER and doesn't have trailing garbage */
+	derlen = i2d_ECDSA_SIG(s, &der);
+	if (derlen != sig_len || memcmp(sigbuf, der, derlen))
+		goto err;
 	ret=ECDSA_do_verify(dgst, dgst_len, s, eckey);
 err:
+	if (derlen > 0)
+		{
+		OPENSSL_cleanse(der, derlen);
+		OPENSSL_free(der);
+		}
 	ECDSA_SIG_free(s);
 	return(ret);
 	}

crypto/x509/x_all.c

@@ -73,6 +73,8 @@
 
 int X509_verify(X509 *a, EVP_PKEY *r)
 	{
+	if (X509_ALGOR_cmp(a->sig_alg, a->cert_info->signature))
+		return 0;
 	return(ASN1_item_verify(ASN1_ITEM_rptr(X509_CINF),a->sig_alg,
 		a->signature,a->cert_info,r));
 	}