Fix Bleichenbacher PKCS #1 1.5 countermeasure.
(The attack against SSL 3.1 and TLS 1.0 is impractical anyway,
otherwise this would be a security relevant patch.)
diff --git a/ssl/s3_srvr.c b/ssl/s3_srvr.c
index dce89bf..0b0ecee 100644
--- a/ssl/s3_srvr.c
+++ b/ssl/s3_srvr.c
@@ -1333,14 +1333,15 @@
i=RSA_private_decrypt((int)n,p,p,rsa,RSA_PKCS1_PADDING);
+ al = -1;
+
if (i != SSL_MAX_MASTER_KEY_LENGTH)
{
al=SSL_AD_DECODE_ERROR;
SSLerr(SSL_F_SSL3_GET_CLIENT_KEY_EXCHANGE,SSL_R_BAD_RSA_DECRYPT);
- goto f_err;
}
- if (!((p[0] == (s->client_version>>8)) && (p[1] == (s->client_version & 0xff))))
+ if ((al == -1) && !((p[0] == (s->client_version>>8)) && (p[1] == (s->client_version & 0xff))))
{
/* The premaster secret must contain the same version number as the
* ClientHello to detect version rollback attacks (strangely, the
@@ -1358,6 +1359,27 @@
}
}
+ if (al != -1)
+ {
+#if 0
+ goto f_err;
+#else
+ /* Some decryption failure -- use random value instead as countermeasure
+ * against Bleichenbacher's attack on PKCS #1 v1.5 RSA padding
+ * (see RFC 2246, section 7.4.7.1).
+ * But note that due to length and protocol version checking, the
+ * attack is impractical anyway (see section 5 in D. Bleichenbacher:
+ * "Chosen Ciphertext Attacks Against Protocols Based on the RSA
+ * Encryption Standard PKCS #1", CRYPTO '98, LNCS 1462, pp. 1-12).
+ */
+ ERR_clear_error();
+ i = SSL_MAX_MASTER_KEY_LENGTH;
+ p[0] = s->client_version >> 8;
+ p[1] = s->client_version & 0xff;
+ RAND_pseudo_bytes(p+2, i-2); /* should be RAND_bytes, but we cannot work around a failure */
+#endif
+ }
+
s->session->master_key_length=
s->method->ssl3_enc->generate_master_secret(s,
s->session->master_key,
