CVE-2021-2351: Oracle Advanced Networking Option RCE Flaw

CVE-2021-2351 Overview

CVE-2021-2351 is a cryptographic vulnerability affecting the Advanced Networking Option component of Oracle Database Server. This vulnerability exists in Oracle's Native Network Encryption (NNE) implementation and allows an unauthenticated attacker with network access via Oracle Net to compromise the Advanced Networking Option component. While the vulnerability requires human interaction and is difficult to exploit, successful attacks can result in a complete takeover of the affected component and may significantly impact additional products due to scope changes.

The vulnerability stems from the use of broken or risky cryptographic algorithms (CWE-327) in the Native Network Encryption implementation. Oracle addressed this issue in the July 2021 Critical Patch Update, which introduced significant changes to Native Network Encryption to prevent the use of weaker ciphers.

Critical Impact

Successful exploitation enables complete takeover of the Advanced Networking Option component, with potential cascading impact on over 100 Oracle products that rely on Oracle Database connectivity. The network-based attack vector combined with the widespread use of Oracle Database makes this a significant enterprise security concern.

Affected Products

• Oracle Advanced Networking Option 12.1.0.2, 12.2.0.1, and 19c
• Oracle WebLogic Server 12.2.1.3.0, 12.2.1.4.0, and 14.1.1.0.0
• Oracle Fusion Middleware 12.2.1.3.0 and 12.2.1.4.0
• Oracle Communications products (multiple versions)
• Oracle Financial Services products (multiple versions)
• Oracle Retail products (multiple versions)
• Oracle Healthcare products (multiple versions)
• Oracle Primavera products (multiple versions)
• Oracle Banking products (multiple versions)
• 100+ additional Oracle enterprise products

Discovery Timeline

• July 2021 - Oracle releases Critical Patch Update addressing CVE-2021-2351
• 2021-07-21 - CVE-2021-2351 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-2351

Vulnerability Analysis

This vulnerability affects Oracle's Native Network Encryption (NNE), a feature that provides data-in-transit encryption for Oracle Database connections. The flaw involves the use of weak or broken cryptographic algorithms that can be exploited by an attacker positioned on the network path between the database client and server.

The attack requires an unauthenticated attacker to have network access via Oracle Net protocol and necessitates human interaction from a victim. Despite these requirements, successful exploitation grants complete control over the Advanced Networking Option component, with potential for impact beyond the vulnerable component itself due to scope changes.

Oracle has documented the changes required to address this vulnerability in support document "Changes in Native Network Encryption with the July 2021 Critical Patch Update" (Doc ID 2791571.1). Organizations are strongly advised to review this documentation when applying patches.

Root Cause

The root cause is classified as CWE-327: Use of a Broken or Risky Cryptographic Algorithm. The Native Network Encryption implementation allowed the negotiation and use of weak cipher suites that do not provide adequate protection against cryptographic attacks. This includes issues with:

• Weak NNE integrity key derivation mechanisms
• Protection mechanism bypass possibilities
• Insufficient cipher strength enforcement during connection negotiation

These weaknesses enable potential man-in-the-middle attacks or cryptographic downgrade scenarios when weak ciphers are permitted.

Attack Vector

The attack is conducted over the network via the Oracle Net protocol, which is the standard communication layer for Oracle Database connections. An attacker must be positioned to intercept or manipulate network traffic between Oracle clients and database servers.

The exploitation scenario involves:

1. An unauthenticated attacker gains network access to the Oracle Net communication path
2. The attacker exploits weaknesses in the Native Network Encryption cipher negotiation
3. Human interaction from a legitimate user initiates a database connection
4. The attacker leverages weak cryptographic protections to compromise the encrypted session
5. Successful exploitation results in confidentiality, integrity, and availability impacts

The attack complexity is classified as high due to the specific conditions required, including network positioning and timing with user-initiated connections.

Detection Methods for CVE-2021-2351

Indicators of Compromise

• Unexpected or suspicious Oracle Net connections using deprecated cipher suites
• Network traffic anomalies between Oracle clients and database servers
• Authentication failures or session anomalies in Oracle database audit logs
• Evidence of cipher downgrade attempts in network protocol analysis
• Unusual patterns in database connection establishment timing

Detection Strategies

• Monitor Oracle Net protocol traffic for use of weak or deprecated encryption algorithms
• Implement network-based detection for man-in-the-middle attack patterns on database connections
• Review Oracle Database audit logs for authentication anomalies and connection failures
• Deploy TLS/SSL inspection at network boundaries to identify encryption downgrades
• Use SentinelOne Singularity platform to detect suspicious process behaviors associated with database connection manipulation

Monitoring Recommendations

• Enable comprehensive Oracle Database auditing including connection and authentication events
• Implement network traffic analysis for Oracle Net protocol communications (port 1521 by default)
• Configure alerts for connections using non-compliant cipher suites after patch application
• Monitor for unexpected network path changes that could indicate MITM positioning
• Establish baseline Oracle connection patterns to detect anomalous behaviors

How to Mitigate CVE-2021-2351

Immediate Actions Required

• Apply the Oracle July 2021 Critical Patch Update or later updates addressing CVE-2021-2351
• Review Oracle support document "Changes in Native Network Encryption with the July 2021 Critical Patch Update" (Doc ID 2791571.1)
• Disable weak cipher suites in Oracle Native Network Encryption configuration
• Audit all Oracle Database instances and dependent products for vulnerability exposure
• Verify that all Oracle client libraries connecting to databases are also updated

Patch Information

Oracle has addressed this vulnerability through multiple Critical Patch Updates:

• Oracle Security Alert - Jul 2021 - Initial patch release
• Oracle Security Alert - Oct 2021 - Additional updates
• Oracle Security Alert - Jan 2022 - Extended product coverage
• Oracle Security Alert - Apr 2022 - Continued remediation
• Oracle Security Alert - Jul 2022 - Further updates
• Oracle Security Alert - Jan 2023 - Latest patches

Given the extensive number of affected Oracle products (100+), organizations should thoroughly inventory all Oracle software and systematically apply patches across Database, Middleware, and Application tiers.

Workarounds

• Restrict network access to Oracle Database servers using firewall rules and network segmentation
• Implement strong network encryption at the transport layer (TLS 1.2 or 1.3) as an additional protection layer
• Disable Native Network Encryption and use TLS-based encryption instead where feasible
• Limit database connection sources to trusted network segments only
• Deploy network intrusion detection systems to monitor for exploitation attempts

# Oracle sqlnet.ora configuration to enforce strong encryption
# Review Oracle documentation for version-specific parameters
SQLNET.ENCRYPTION_SERVER = required
SQLNET.ENCRYPTION_TYPES_SERVER = (AES256)
SQLNET.CRYPTO_CHECKSUM_SERVER = required
SQLNET.CRYPTO_CHECKSUM_TYPES_SERVER = (SHA256)