From 18c02492138d1eb8b6548cb26e7b625fb2414a2a Mon Sep 17 00:00:00 2001
From: Tomas Mraz <tomas@openssl.org>
Date: Fri, 22 Dec 2023 16:25:56 +0100
Subject: [PATCH] Limit the execution time of RSA public key check

Fixes CVE-2023-6237

If a large and incorrect RSA public key is checked with
EVP_PKEY_public_check() the computation could take very long time
due to no limit being applied to the RSA public key size and
unnecessarily high number of Miller-Rabin algorithm rounds
used for non-primality check of the modulus.

Now the keys larger than 16384 bits (OPENSSL_RSA_MAX_MODULUS_BITS)
will fail the check with RSA_R_MODULUS_TOO_LARGE error reason.
Also the number of Miller-Rabin rounds was set to 5.

Reviewed-by: Neil Horman <nhorman@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/23243)

(cherry picked from commit e09fc1d746a4fd15bb5c3d7bbbab950aadd005db)
---
 crypto/rsa/rsa_sp800_56b_check.c              |  8 +++-
 test/recipes/91-test_pkey_check.t             |  2 +-
 .../91-test_pkey_check_data/rsapub_17k.pem    | 48 +++++++++++++++++++
 3 files changed, 56 insertions(+), 2 deletions(-)
 create mode 100644 test/recipes/91-test_pkey_check_data/rsapub_17k.pem

diff --git a/crypto/rsa/rsa_sp800_56b_check.c b/crypto/rsa/rsa_sp800_56b_check.c
index fc8f19b487..bcbdd24fb8 100644
--- a/crypto/rsa/rsa_sp800_56b_check.c
+++ b/crypto/rsa/rsa_sp800_56b_check.c
@@ -289,6 +289,11 @@ int ossl_rsa_sp800_56b_check_public(const RSA *rsa)
         return 0;
 
     nbits = BN_num_bits(rsa->n);
+    if (nbits > OPENSSL_RSA_MAX_MODULUS_BITS) {
+        ERR_raise(ERR_LIB_RSA, RSA_R_MODULUS_TOO_LARGE);
+        return 0;
+    }
+
 #ifdef FIPS_MODULE
     /*
      * (Step a): modulus must be 2048 or 3072 (caveat from SP800-56Br1)
@@ -324,7 +329,8 @@ int ossl_rsa_sp800_56b_check_public(const RSA *rsa)
         goto err;
     }
 
-    ret = ossl_bn_miller_rabin_is_prime(rsa->n, 0, ctx, NULL, 1, &status);
+    /* Highest number of MR rounds from FIPS 186-5 Section B.3 Table B.1 */
+    ret = ossl_bn_miller_rabin_is_prime(rsa->n, 5, ctx, NULL, 1, &status);
 #ifdef FIPS_MODULE
     if (ret != 1 || status != BN_PRIMETEST_COMPOSITE_NOT_POWER_OF_PRIME) {
 #else
diff --git a/test/recipes/91-test_pkey_check.t b/test/recipes/91-test_pkey_check.t
index dc7cc64533..f8088df14d 100644
--- a/test/recipes/91-test_pkey_check.t
+++ b/test/recipes/91-test_pkey_check.t
@@ -70,7 +70,7 @@ push(@positive_tests, (
     "dhpkey.pem"
     )) unless disabled("dh");
 
-my @negative_pubtests = ();
+my @negative_pubtests = ("rsapub_17k.pem");  # Too big RSA public key
 
 push(@negative_pubtests, (
     "dsapub_noparam.der"
diff --git a/test/recipes/91-test_pkey_check_data/rsapub_17k.pem b/test/recipes/91-test_pkey_check_data/rsapub_17k.pem
new file mode 100644
index 0000000000..9a2eaedaf1
--- /dev/null
+++ b/test/recipes/91-test_pkey_check_data/rsapub_17k.pem
@@ -0,0 +1,48 @@
+-----BEGIN PUBLIC KEY-----
+MIIIbzANBgkqhkiG9w0BAQEFAAOCCFwAMIIIVwKCCE4Ang+cE5H+hg3RbapDAHqR
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+-----END PUBLIC KEY-----
-- 
2.36.1