CVE-2021-38296: Apache Spark Information Disclosure Flaw

CVE-2021-38296 Overview

Apache Spark versions 3.1.2 and earlier contain a cryptographic vulnerability in their end-to-end RPC connection encryption implementation. The vulnerability exists in the bespoke mutual authentication protocol used when spark.authenticate and spark.network.crypto.enabled are enabled. This flawed protocol allows attackers to perform full encryption key recovery through an initial interactive attack, subsequently enabling offline decryption of captured plaintext traffic.

Critical Impact

Attackers can recover encryption keys through an interactive attack, enabling complete decryption of encrypted RPC communications between Spark components. This could expose sensitive data processed through Spark clusters including credentials, business data, and internal communications.

Affected Products

• Apache Spark versions 3.1.2 and earlier
• Oracle Financial Services Crime and Compliance Management Studio 8.0.8.2.0
• Oracle Financial Services Crime and Compliance Management Studio 8.0.8.3.0

Discovery Timeline

• 2022-03-10 - CVE CVE-2021-38296 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-38296

Vulnerability Analysis

This vulnerability is classified as CWE-294: Authentication Bypass by Capture-replay. The core issue lies in Apache Spark's custom mutual authentication protocol implementation used for RPC connection encryption. When administrators enable end-to-end encryption via the spark.authenticate and spark.network.crypto.enabled configuration options, the system uses a bespoke cryptographic protocol that contains fundamental design weaknesses.

The flawed authentication mechanism allows an attacker positioned on the network to perform an interactive attack against the authentication handshake. Upon successful completion of this initial attack phase, the attacker obtains sufficient cryptographic material to fully recover the encryption key used to protect the RPC communications. This represents a complete break of the encryption scheme's confidentiality guarantees.

Root Cause

The root cause is a weak custom mutual authentication protocol design in Apache Spark's RPC encryption feature. Rather than using a well-established and vetted cryptographic protocol, Spark implemented a bespoke authentication scheme that does not adequately protect the encryption key material during the handshake process. This custom protocol fails to prevent key recovery attacks, violating fundamental cryptographic security principles.

It is important to note that this vulnerability does not affect other Spark security mechanisms including spark.authenticate.enableSaslEncryption, spark.io.encryption.enabled, spark.ssl, and spark.ui.strictTransportSecurity, which use different and properly implemented security protocols.

Attack Vector

The attack requires network access to intercept communications between Spark components. An attacker must be able to observe and potentially interact with the RPC connection handshake between Spark nodes. The attack proceeds in two phases:

1. Interactive Phase: The attacker actively participates in or manipulates the authentication protocol exchange, gathering cryptographic material from the handshake messages.

2. Offline Decryption Phase: Using the recovered key material, the attacker can decrypt previously captured encrypted traffic without any further interaction with the target systems.

This network-based attack vector allows attackers to compromise the confidentiality of all RPC communications without requiring any user interaction or elevated privileges on the target systems.

Detection Methods for CVE-2021-38296

Indicators of Compromise

• Unusual network traffic patterns during Spark RPC connection establishment that may indicate handshake manipulation
• Multiple connection attempts or abnormal authentication sequence timing between Spark nodes
• Evidence of network sniffing or packet capture activities targeting Spark cluster communication ports
• Unexpected connections to Spark nodes from unauthorized network segments

Detection Strategies

• Monitor Spark cluster network traffic for anomalous authentication patterns or replayed handshake messages
• Implement network intrusion detection rules to identify potential key recovery attack patterns against Spark RPC endpoints
• Audit Spark configuration files to identify clusters using the vulnerable spark.authenticate and spark.network.crypto.enabled settings
• Deploy network flow analysis to detect unauthorized interception of inter-node Spark communications

Monitoring Recommendations

• Enable detailed logging on Spark cluster nodes to capture authentication events and connection metadata
• Implement network traffic baseline monitoring for Spark RPC ports to detect anomalies indicative of active exploitation
• Configure alerts for failed or abnormal authentication attempts between Spark cluster components
• Use SentinelOne Singularity platform to monitor for suspicious network behavior and potential lateral movement within Spark infrastructure

How to Mitigate CVE-2021-38296

Immediate Actions Required

• Upgrade Apache Spark to version 3.1.3 or later which contains the security fix for this vulnerability
• Review and update Oracle Financial Services Crime and Compliance Management Studio installations per the Oracle July 2022 Security Alert
• Audit current Spark deployments to identify which clusters have spark.authenticate and spark.network.crypto.enabled enabled
• Consider temporarily using alternative security mechanisms such as spark.authenticate.enableSaslEncryption or spark.ssl while planning upgrades

Patch Information

Apache has released Spark version 3.1.3 which addresses this vulnerability by fixing the flawed mutual authentication protocol. Administrators should upgrade all affected Spark installations to version 3.1.3 or later. Oracle has also released patches for affected Financial Services Crime and Compliance Management Studio versions through their July 2022 Critical Patch Update.

For detailed patch information, consult the Apache Mailing List Thread and the Oracle July 2022 Security Alert.

Workarounds

• Disable the vulnerable encryption settings (spark.authenticate and spark.network.crypto.enabled) and use alternative security mechanisms like spark.ssl for transport encryption
• Implement network segmentation to isolate Spark cluster communications from untrusted network segments
• Deploy network-level encryption such as IPsec or VPN tunnels between Spark nodes as an additional security layer
• Restrict network access to Spark RPC ports using firewall rules to minimize exposure to potential attackers

The recommended mitigation approach involves reviewing your Spark cluster configuration to determine which encryption settings are in use. If the vulnerable settings are enabled, either upgrade to the patched version or switch to alternative security mechanisms that are not affected by this vulnerability.