From bb4928317b43a21288206a181259c3655b51acaf Mon Sep 17 00:00:00 2001
From: michaelpaliy <michael.paliy@niceactimize.com>
Date: Sat, 15 Apr 2023 17:16:15 +0300
Subject: [PATCH] fix jwk exponent constraint

---
 src/jwks.cc                                   |  4 +--
 .../jwks_rsa_non_standard_exponent.txt        |  2 ++
 test/fuzz/corpus_format_test.cc               |  2 +-
 test/jwks_test.cc                             | 36 ++++++++++++++++++-
 4 files changed, 40 insertions(+), 4 deletions(-)
 create mode 100644 test/fuzz/corpus/jwt_verify_lib_fuzz_test/jwks_rsa_non_standard_exponent.txt

diff --git a/src/jwks.cc b/src/jwks.cc
index a81b576..0a64b8e 100644
--- a/src/jwks.cc
+++ b/src/jwks.cc
@@ -104,8 +104,8 @@ class KeyGetter : public WithStatus {
       updateStatus(Status::JwksRsaParseError);
       return nullptr;
     }
-    if (BN_cmp_word(rsa->e, 3) != 0 && BN_cmp_word(rsa->e, 65537) != 0) {
-      // non-standard key; reject it early.
+    if (BN_cmp_word(rsa->e, 3) < 0) {
+      // invalid key exponent; reject it early.
       updateStatus(Status::JwksRsaParseError);
       return nullptr;
     }
diff --git a/test/fuzz/corpus/jwt_verify_lib_fuzz_test/jwks_rsa_non_standard_exponent.txt b/test/fuzz/corpus/jwt_verify_lib_fuzz_test/jwks_rsa_non_standard_exponent.txt
new file mode 100644
index 0000000..83d5fde
--- /dev/null
+++ b/test/fuzz/corpus/jwt_verify_lib_fuzz_test/jwks_rsa_non_standard_exponent.txt
@@ -0,0 +1,2 @@
+jwt: "eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJzb21lIjoicGF5bG9hZCJ9.Xi5bFv0m3_5t4tzhjY0AuM_zFrZwAVz0-_x8wIa4Pis8gkYi-5OBo0pPU5rYRTl3auTfS83AtBymBHr0r98vHWuruA07UGlDf_0TvurSAczHRr7Zp4k7K4easqcHecnIqdMXFZVG9-EW0QqVLduezIIPcfNLjwHiz5XyfKisuF8eV5WILWO7HVRTBmn_26W_vRP4QKDtwO5kXujQ60eLZbRzfa9QnUS_LVe9khOWzAQphot5peOs4iLGsc6H4-RJP-tYGxWojTI8LlmN23kj7IcvJWIJmnIicTJfmV-O70SldHmhiFtACXkBvbk32U02Ck0_crPtmIZ4nTxDO5ydKA"
+jwks: '{"keys":[{"n":"q2ortveItN3-AseXStq37n9XW4lcWOanOFfSN6F65Pj9Su3Maf4zUuIpaUDrLREvNQTw3ZEVwbYxgjk6RsVbTPkmVOvj9m8U9QcyF9erMoyDx7xAkahpw2bqXz_d6CGnORlflnEudmlgHEVe3t3eFN73LHqDlrkWYV_6TV3iSxLOAeNTNWCC1rrNLLlgFeWVYfG4q_n4evGG3Pm944MFjXySQQdwvynokH6VY0rO-V16LQiEaC9r9mWcpfYFrg_wK4OJxWyr6GPb1H_TvkB089fjQ2fablznfnaZvi-mp1nV1Pl19Bfv4hEcue6QxZvAZBdGXApqUzZjoGFBi637OQ","e":"Iw","kty":"RSA","alg": "RS256","use": "sig","kid":"Z_oCEjzMXWjatoGK3hKZCFzw4AuZEt3SRMdUtuw3WwI"}]}'
diff --git a/test/fuzz/corpus_format_test.cc b/test/fuzz/corpus_format_test.cc
index 18259f6..6339907 100644
--- a/test/fuzz/corpus_format_test.cc
+++ b/test/fuzz/corpus_format_test.cc
@@ -40,7 +40,7 @@ std::string ReadTestBaseline(const std::string& input_file_name) {
 // to be more efficient.
 // This test verifies the following corpus files satisfy above conditions.
 TEST(JwksParseTest, FuzzTestJwksCorpusFile) {
-  std::vector<std::string> files = {"jwks_ec.txt",   "jwks_rsa.txt",
+  std::vector<std::string> files = {"jwks_ec.txt",   "jwks_rsa.txt", "jwks_rsa_non_standard_exponent.txt",
                                     "jwks_hmac.txt", "jwks_okp.txt",
                                     "jwks_x509.txt", "jwks_pem.txt"};
   for (const auto& file : files) {
diff --git a/test/jwks_test.cc b/test/jwks_test.cc
index 593b6fb..96d8461 100644
--- a/test/jwks_test.cc
+++ b/test/jwks_test.cc
@@ -425,7 +425,7 @@ TEST(JwksParseTest, JwksECWrongXY) {
   EXPECT_EQ(jwks->getStatus(), Status::JwksEcParseError);
 }
 
-TEST(JwksParseTest, JwksRSAWrongNE) {
+TEST(JwksParseTest, ValidLargeExponent) {
   const std::string jwks_text = R"(
      {
         "keys": [
@@ -437,6 +437,40 @@ TEST(JwksParseTest, JwksRSAWrongNE) {
            }
         ]
      }
+)";
+  auto jwks = Jwks::createFrom(jwks_text, Jwks::JWKS);
+  EXPECT_EQ(jwks->getStatus(), Status::Ok);
+}
+
+TEST(JwksParseTest, ValidExponentIs3) {
+  const std::string jwks_text = R"(
+     {
+        "keys": [
+           {
+               "kty": "RSA",
+               "n": "EB54wykhS7YJFD6RYJNnwbW",
+               "e": "Aw==",
+               "alg": "RS256"
+           }
+        ]
+     }
+)";
+  auto jwks = Jwks::createFrom(jwks_text, Jwks::JWKS);
+  EXPECT_EQ(jwks->getStatus(), Status::Ok);
+}
+
+TEST(JwksParseTest, JwksRSAWrongNE) {
+  const std::string jwks_text = R"(
+     {
+        "keys": [
+           {
+               "kty": "RSA",
+               "n": "EB54wykhS7YJFD6RYJNnwbW",
+               "e": "Ag==",
+               "alg": "RS256"
+           }
+        ]
+     }
 )";
   auto jwks = Jwks::createFrom(jwks_text, Jwks::JWKS);
   EXPECT_EQ(jwks->getStatus(), Status::JwksRsaParseError);