Patches backported from later development version of OpenSSH which prevent
(instead of just mitigating through connection limits) the Bleichenbacher attack which can lead to guessing of the server key (not host key) by regenerating it when an RSA failure is detected. Reviewed by: rwatson
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parent
f1a87e83ee
commit
a09221f83c
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=72397
@ -161,7 +161,7 @@ rsa_public_encrypt(BIGNUM *out, BIGNUM *in, RSA *key)
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xfree(inbuf);
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}
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void
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int
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rsa_private_decrypt(BIGNUM *out, BIGNUM *in, RSA *key)
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{
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unsigned char *inbuf, *outbuf;
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@ -175,15 +175,16 @@ rsa_private_decrypt(BIGNUM *out, BIGNUM *in, RSA *key)
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BN_bn2bin(in, inbuf);
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if ((len = RSA_private_decrypt(ilen, inbuf, outbuf, key,
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RSA_PKCS1_PADDING)) <= 0)
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fatal("rsa_private_decrypt() failed.");
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BN_bin2bn(outbuf, len, out);
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RSA_PKCS1_PADDING)) <= 0) {
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error("rsa_private_decrypt() failed");
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} else {
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BN_bin2bn(outbuf, len, out);
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}
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memset(outbuf, 0, olen);
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memset(inbuf, 0, ilen);
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xfree(outbuf);
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xfree(inbuf);
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return len;
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}
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/* Set whether to output verbose messages during key generation. */
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@ -32,6 +32,6 @@ void rsa_set_verbose __P((int verbose));
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int rsa_alive __P((void));
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void rsa_public_encrypt __P((BIGNUM * out, BIGNUM * in, RSA * prv));
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void rsa_private_decrypt __P((BIGNUM * out, BIGNUM * in, RSA * prv));
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int rsa_private_decrypt __P((BIGNUM * out, BIGNUM * in, RSA * prv));
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#endif /* RSA_H */
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@ -194,7 +194,8 @@ process_authentication_challenge1(SocketEntry *e)
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private = lookup_private_key(key, NULL, 1);
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if (private != NULL) {
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/* Decrypt the challenge using the private key. */
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rsa_private_decrypt(challenge, challenge, private->rsa);
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if (rsa_private_decrypt(challenge, challenge, private->rsa) <= 0)
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goto failure;
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/* The response is MD5 of decrypted challenge plus session id. */
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len = BN_num_bytes(challenge);
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@ -152,14 +152,17 @@ respond_to_rsa_challenge(BIGNUM * challenge, RSA * prv)
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int i, len;
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/* Decrypt the challenge using the private key. */
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rsa_private_decrypt(challenge, challenge, prv);
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/* XXX think about Bleichenbacher, too */
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if (rsa_private_decrypt(challenge, challenge, prv) <= 0)
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packet_disconnect(
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"respond_to_rsa_challenge: rsa_private_decrypt failed");
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/* Compute the response. */
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/* The response is MD5 of decrypted challenge plus session id. */
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len = BN_num_bytes(challenge);
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if (len <= 0 || len > sizeof(buf))
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packet_disconnect("respond_to_rsa_challenge: bad challenge length %d",
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len);
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packet_disconnect(
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"respond_to_rsa_challenge: bad challenge length %d", len);
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memset(buf, 0, sizeof(buf));
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BN_bn2bin(challenge, buf + sizeof(buf) - len);
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@ -1108,6 +1108,7 @@ do_ssh1_kex()
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{
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int i, len;
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int plen, slen;
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int rsafail = 0;
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BIGNUM *session_key_int;
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unsigned char session_key[SSH_SESSION_KEY_LENGTH];
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unsigned char cookie[8];
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@ -1229,7 +1230,7 @@ do_ssh1_kex()
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* with larger modulus first).
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*/
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if (BN_cmp(sensitive_data.private_key->n, sensitive_data.host_key->n) > 0) {
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/* Private key has bigger modulus. */
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/* Server key has bigger modulus. */
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if (BN_num_bits(sensitive_data.private_key->n) <
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BN_num_bits(sensitive_data.host_key->n) + SSH_KEY_BITS_RESERVED) {
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fatal("do_connection: %s: private_key %d < host_key %d + SSH_KEY_BITS_RESERVED %d",
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@ -1238,10 +1239,12 @@ do_ssh1_kex()
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BN_num_bits(sensitive_data.host_key->n),
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SSH_KEY_BITS_RESERVED);
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}
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rsa_private_decrypt(session_key_int, session_key_int,
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sensitive_data.private_key);
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rsa_private_decrypt(session_key_int, session_key_int,
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sensitive_data.host_key);
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if (rsa_private_decrypt(session_key_int, session_key_int,
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sensitive_data.private_key) <= 0)
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rsafail++;
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if (rsa_private_decrypt(session_key_int, session_key_int,
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sensitive_data.host_key) <= 0)
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rsafail++;
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} else {
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/* Host key has bigger modulus (or they are equal). */
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if (BN_num_bits(sensitive_data.host_key->n) <
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@ -1252,10 +1255,12 @@ do_ssh1_kex()
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BN_num_bits(sensitive_data.private_key->n),
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SSH_KEY_BITS_RESERVED);
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}
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rsa_private_decrypt(session_key_int, session_key_int,
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sensitive_data.host_key);
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rsa_private_decrypt(session_key_int, session_key_int,
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sensitive_data.private_key);
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if (rsa_private_decrypt(session_key_int, session_key_int,
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sensitive_data.host_key) < 0)
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rsafail++;
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if (rsa_private_decrypt(session_key_int, session_key_int,
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sensitive_data.private_key) < 0)
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rsafail++;
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}
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compute_session_id(session_id, cookie,
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@ -1270,14 +1275,29 @@ do_ssh1_kex()
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* least significant 256 bits of the integer; the first byte of the
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* key is in the highest bits.
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*/
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BN_mask_bits(session_key_int, sizeof(session_key) * 8);
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len = BN_num_bytes(session_key_int);
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if (len < 0 || len > sizeof(session_key))
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fatal("do_connection: bad len from %s: session_key_int %d > sizeof(session_key) %d",
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get_remote_ipaddr(),
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len, sizeof(session_key));
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memset(session_key, 0, sizeof(session_key));
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BN_bn2bin(session_key_int, session_key + sizeof(session_key) - len);
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if (!rsafail) {
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BN_mask_bits(session_key_int, sizeof(session_key) * 8);
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len = BN_num_bytes(session_key_int);
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if (len < 0 || len > sizeof(session_key)) {
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error("do_connection: bad session key len from %s: "
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"session_key_int %d > sizeof(session_key) %d",
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get_remote_ipaddr(), len, sizeof(session_key));
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rsafail++;
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} else {
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memset(session_key, 0, sizeof(session_key));
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BN_bn2bin(session_key_int,
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session_key + sizeof(session_key) - len);
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}
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}
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if (rsafail) {
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log("do_connection: generating a fake encryption key");
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for (i = 0; i < SSH_SESSION_KEY_LENGTH; i++) {
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if (i % 4 == 0)
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rand = arc4random();
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session_key[i] = rand & 0xff;
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rand >>= 8;
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}
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}
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/* Destroy the decrypted integer. It is no longer needed. */
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BN_clear_free(session_key_int);
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