Advisory ID: SYSS-2021-062  
Product: Database  
Manufacturer: Oracle  
Affected Version(s):,, 19c  
Tested Version(s): 18c  
Vulnerability Type: Inadequate Encryption Strength (CWE-326)  
Risk Level: Medium  
Solution Status: Fixed  
Manufacturer Notification: 2021-03-17  
Solution Date: 2021-08-07  
Public Disclosure: 2021-12-10  
CVE Reference: CVE-2021-2351  
Author of Advisory: Moritz Bechler, SySS GmbH  
Oracle Database is a general purpose relational database management  
system (RDMBS).  
The manufacturer describes the product as follows (see [1]):  
"Oracle database products offer customers cost-optimized and high-performance   
versions of Oracle Database, the world's leading converged, multi-model   
database management system, as well as in-memory, NoSQL and MySQL databases.  
Oracle Autonomous Database, available on premises via Oracle Cloud@Customer   
or in the Oracle Cloud Infrastructure, enables customers to simplify relational   
database environments and reduce management workloads."  
To protect the client/server communication, a proprietary security protocol   
"Native Network Encryption" (NNE) is used.   
A TLS-based alternative can optionally be configured.  
NNE's integrity protection mechanism deliberately weakens the key used   
for computing per-packet message authentication codes (MACs).   
Vulnerability Details:  
When analyzing the protocol details, SySS found out that depending on  
the selected hash algorithms, one of two key generation schemes is used.  
Both are seeded with material from the established session key.  
However, even for the AES-based key generator, which is used when modern   
cryptographic primitives are selected, the session key is truncated to  
40 bits.  
For more details on the protocol and MAC computation, refer to our  
paper [4].  
Brute-force cracking of that key, for example if only integrity but no   
encryption is enabled, is likely possible and allows malicious  
manipulation of transmitted database commands or data.  
Proof of Concept (PoC):  
The initialization of the key generator, as originally implemented, can   
be described with the following Python code, where SK is the established  
session key, and the initialization vector (IV) was exchanged in  
clear text during NNE negotiation.   
mk = SK[0:5] + b'\xFF' + b'\x00' * 10  
self.m =, AES.MODE_CBC, iv=IV[0:16]) = b'\x00'*32 = s = self.m.encrypt(  
self.m =[0:16], AES.MODE_CBC, iv=s[16:32])  
k1 = s[0:5] + b'\xB4' + s[6:16]  
self.s2c =, AES.MODE_CBC, iv=s[16:32])  
self.s2cs = b'\x00' * 32  
k2 = s[0:5] + b'\x5A' + s[6:16]  
self.c2s =, AES.MODE_CBC, iv=s[16:32])  
self.c2ss = b'\x00' * 32  
A per-packet key "k" is then generated like  
self.c2ss = k = self.c2s.encrypt(self.c2ss)  
and appended to the packet data as well as hashed using the selected hash algorithm.  
Update the Oracle Database servers and clients to the patched versions.  
Enforce usage of a secured protocol version by setting the following options:  
Or use TLS-based transport security instead of Native Network Encryption.  
More information: (customer account required)  
Disclosure Timeline:  
2013-03-02: Vulnerability discovered  
2021-03-17: Vulnerability reported to manufacturer  
2021-07-20: Initial patch release by manufacturer,   
2021-08-07: Final patches released by manufacturer  
2021-12-10: Public disclosure of vulnerability  
[1] Product website for Oracle Database  
[2] SySS Security Advisory SYSS-2021-062  
[3] SySS Responsible Disclosure Policy  
[4] Paper "Oracle Native Network Encryption"  
This security vulnerability was found by Moritz Bechler of SySS GmbH.  
Public Key:  
Key ID: 0x768EFE2BB3E53DDA  
Key Fingerprint: 2C8F F101 9D77 BDE6 465E CCC2 768E FE2B B3E5 3DDA  
The information provided in this security advisory is provided "as is"   
and without warranty of any kind. Details of this security advisory may  
be updated in order to provide as accurate information as possible. The  
latest version of this security advisory is available on the SySS website.  
Creative Commons - Attribution (by) - Version 3.0