commit 08dbad8552ecca85d3e38072f94eb864b143d218
Author: Niklas Hambüchen <mail@nh2.me>
Date:   Mon Jan 22 12:52:06 2024 +0000

    Cherry-pick fix for CVE-2023-49083
    
    Cherry-Picked-From: f09c261ca10a31fe41b1262306db7f8f1da0e48a
    Cherry-Picked-By: Niklas Hambüchen <mail@nh2.me>

diff --git a/src/cryptography/hazmat/backends/openssl/backend.py b/src/cryptography/hazmat/backends/openssl/backend.py
index a3fe1bce4..58e7207c4 100644
--- a/src/cryptography/hazmat/backends/openssl/backend.py
+++ b/src/cryptography/hazmat/backends/openssl/backend.py
@@ -2383,9 +2383,12 @@ class Backend:
                 _Reasons.UNSUPPORTED_SERIALIZATION,
             )
 
+        certs: list[x509.Certificate] = []
+        if p7.d.sign == self._ffi.NULL:
+            return certs
+
         sk_x509 = p7.d.sign.cert
         num = self._lib.sk_X509_num(sk_x509)
-        certs = []
         for i in range(num):
             x509 = self._lib.sk_X509_value(sk_x509, i)
             self.openssl_assert(x509 != self._ffi.NULL)
diff --git a/tests/hazmat/primitives/test_pkcs7.py b/tests/hazmat/primitives/test_pkcs7.py
index 4e61c5ef5..d8170bfb9 100644
--- a/tests/hazmat/primitives/test_pkcs7.py
+++ b/tests/hazmat/primitives/test_pkcs7.py
@@ -89,6 +89,12 @@ class TestPKCS7Loading:
                 mode="rb",
             )
 
+    def test_load_pkcs7_empty_certificates(self, backend):
+        der = b"\x30\x0B\x06\x09\x2A\x86\x48\x86\xF7\x0D\x01\x07\x02"
+
+        certificates = pkcs7.load_der_pkcs7_certificates(der)
+        assert certificates == []
+
 
 # We have no public verification API and won't be adding one until we get
 # some requirements from users so this function exists to give us basic