Check DSA parameters for excessive sizes before validating

This avoids overly long computation of various validation checks. Fixes CVE-2024-4603 Reviewed-by: Paul Dale <ppzgs1@gmail.com> Reviewed-by: Matt Caswell <matt@openssl.org> Reviewed-by: Neil Horman <nhorman@openssl.org> Reviewed-by: Shane Lontis <shane.lontis@oracle.com> (Merged from #24346) (cherry picked from commit 85ccbab)
openssl · May 16, 2024 · 9c39b38 · 9c39b38
1 parent 0b49dde
commit 9c39b38
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diff --git a/CHANGES.md b/CHANGES.md
@@ -24,6 +24,23 @@ OpenSSL 3.1
 
 ### Changes between 3.1.5 and 3.1.6 [xx XXX xxxx]
 
+ * Fixed an issue where checking excessively long DSA keys or parameters may
+   be very slow.
+
+   Applications that use the functions EVP_PKEY_param_check() or
+   EVP_PKEY_public_check() to check a DSA public key or DSA parameters may
+   experience long delays. Where the key or parameters that are being checked
+   have been obtained from an untrusted source this may lead to a Denial of
+   Service.
+
+   To resolve this issue DSA keys larger than OPENSSL_DSA_MAX_MODULUS_BITS
+   will now fail the check immediately with a DSA_R_MODULUS_TOO_LARGE error
+   reason.
+
+   ([CVE-2024-4603])
+
+   *Tomáš Mráz*
+
  * Fixed an issue where some non-default TLS server configurations can cause
    unbounded memory growth when processing TLSv1.3 sessions. An attacker may
    exploit certain server configurations to trigger unbounded memory growth that

diff --git a/crypto/dsa/dsa_check.c b/crypto/dsa/dsa_check.c
@@ -19,8 +19,34 @@
 #include "dsa_local.h"
 #include "crypto/dsa.h"
 
+static int dsa_precheck_params(const DSA *dsa, int *ret)
+{
+    if (dsa->params.p == NULL || dsa->params.q == NULL) {
+        ERR_raise(ERR_LIB_DSA, DSA_R_BAD_FFC_PARAMETERS);
+        *ret = FFC_CHECK_INVALID_PQ;
+        return 0;
+    }
+
+    if (BN_num_bits(dsa->params.p) > OPENSSL_DSA_MAX_MODULUS_BITS) {
+        ERR_raise(ERR_LIB_DSA, DSA_R_MODULUS_TOO_LARGE);
+        *ret = FFC_CHECK_INVALID_PQ;
+        return 0;
+    }
+
+    if (BN_num_bits(dsa->params.q) >= BN_num_bits(dsa->params.p)) {
+        ERR_raise(ERR_LIB_DSA, DSA_R_BAD_Q_VALUE);
+        *ret = FFC_CHECK_INVALID_PQ;
+        return 0;
+    }
+
+    return 1;
+}
+
 int ossl_dsa_check_params(const DSA *dsa, int checktype, int *ret)
 {
+    if (!dsa_precheck_params(dsa, ret))
+        return 0;
+
     if (checktype == OSSL_KEYMGMT_VALIDATE_QUICK_CHECK)
         return ossl_ffc_params_simple_validate(dsa->libctx, &dsa->params,
                                                FFC_PARAM_TYPE_DSA, ret);
@@ -39,6 +65,9 @@ int ossl_dsa_check_params(const DSA *dsa, int checktype, int *ret)
  */
 int ossl_dsa_check_pub_key(const DSA *dsa, const BIGNUM *pub_key, int *ret)
 {
+    if (!dsa_precheck_params(dsa, ret))
+        return 0;
+
     return ossl_ffc_validate_public_key(&dsa->params, pub_key, ret)
            && *ret == 0;
 }
@@ -50,6 +79,9 @@ int ossl_dsa_check_pub_key(const DSA *dsa, const BIGNUM *pub_key, int *ret)
  */
 int ossl_dsa_check_pub_key_partial(const DSA *dsa, const BIGNUM *pub_key, int *ret)
 {
+    if (!dsa_precheck_params(dsa, ret))
+        return 0;
+
     return ossl_ffc_validate_public_key_partial(&dsa->params, pub_key, ret)
            && *ret == 0;
 }
@@ -58,8 +90,10 @@ int ossl_dsa_check_priv_key(const DSA *dsa, const BIGNUM *priv_key, int *ret)
 {
     *ret = 0;
 
-    return (dsa->params.q != NULL
-            && ossl_ffc_validate_private_key(dsa->params.q, priv_key, ret));
+    if (!dsa_precheck_params(dsa, ret))
+        return 0;
+
+    return ossl_ffc_validate_private_key(dsa->params.q, priv_key, ret);
 }
 
 /*
@@ -72,8 +106,10 @@ int ossl_dsa_check_pairwise(const DSA *dsa)
     BN_CTX *ctx = NULL;
     BIGNUM *pub_key = NULL;
 
-    if (dsa->params.p == NULL
-        || dsa->params.g == NULL
+    if (!dsa_precheck_params(dsa, &ret))
+        return 0;
+
+    if (dsa->params.g == NULL
         || dsa->priv_key == NULL
         || dsa->pub_key == NULL)
         return 0;

diff --git a/test/recipes/15-test_dsaparam_data/invalid/p10240_q256_too_big.pem b/test/recipes/15-test_dsaparam_data/invalid/p10240_q256_too_big.pem
@@ -0,0 +1,57 @@
+-----BEGIN DSA PARAMETERS-----
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+vKuje86bePD6kD/LH3wmkA==
+-----END DSA PARAMETERS-----