CVE-2021-3422 in Splunk
Summary
by MITRE • 03/25/2022
The lack of validation of a key-value field in the Splunk-to-Splunk protocol results in a denial-of-service in Splunk Enterprise instances configured to index Universal Forwarder traffic. See https://docs.splunk.com/Documentation/Splunk/latest/Forwarding/Enableareceiver for more information on configuring an indexer to listen for UF traffic. It does not impact Universal Forwarders. When Splunk forwarding is secured using TLS or a Token, the attack requires compromising the certificate or token, or both. As a partial mitigation and a security best practice, see https://docs.splunk.com/Documentation/Splunk/latest/Security/ConfigureSplunkforwardingtousesignedcertificates and https://docs.splunk.com/Documentation/Forwarder/latest/Forwarder/Controlforwarderaccess. Implementation of either or both reduces the severity to Medium.
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Analysis
by VulDB Data Team • 03/27/2022
The vulnerability identified as CVE-2021-3422 represents a critical denial-of-service weakness within Splunk Enterprise systems that process Universal Forwarder traffic. This flaw exists within the Splunk-to-Splunk protocol implementation where insufficient validation occurs for key-value fields during message processing. The vulnerability specifically targets Splunk Enterprise instances configured as indexers that receive data from Universal Forwarders, creating a pathway for malicious actors to disrupt normal operations through carefully crafted malformed messages. The technical nature of this issue stems from inadequate input sanitization mechanisms that fail to properly validate the structure and content of key-value pairs transmitted between Splunk components. This weakness operates at the protocol level, affecting the core message handling functionality that enables distributed log aggregation and monitoring capabilities essential to enterprise security operations.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the integrity of security monitoring systems that depend on continuous data flow from distributed sources. When exploited, the vulnerability can cause Splunk Enterprise instances to become unresponsive or crash entirely, effectively removing the organization's ability to monitor and analyze security events in real-time. The attack vector requires sending specially crafted messages to the indexer component, which then processes these malformed inputs without proper validation, leading to resource exhaustion or application instability. This vulnerability particularly affects organizations that rely heavily on Splunk for security information and event management, as the disruption can mask actual security incidents while the system remains unavailable. The severity classification reflects the potential for widespread operational impact across multiple systems within an organization's infrastructure that depend on Splunk for centralized log management and threat detection.
The vulnerability's exploitation requires minimal prerequisites when Splunk forwarding is not properly secured through TLS encryption or token authentication mechanisms. However, the implementation of proper security controls significantly reduces the attack surface and severity of potential exploitation. Organizations implementing TLS certificates or token-based authentication create additional barriers that require attackers to compromise these security layers before successfully exploiting the vulnerability. This aligns with security best practices outlined in industry standards and frameworks where layered defense mechanisms are recommended to reduce overall risk exposure. The mitigation strategies include implementing signed certificates for Splunk forwarding as specified in Splunk documentation, along with controlling forwarder access through proper authentication mechanisms. These controls map directly to common ATT&CK techniques related to credential access and privilege escalation, where the vulnerability represents a potential entry point for adversaries seeking to disrupt security operations. The CWE classification for this vulnerability would likely fall under CWE-20 Input Validation, specifically related to insufficient validation of key-value pairs in network protocols. The attack surface is reduced when proper certificate management and token-based authentication are implemented, moving the vulnerability severity from high to medium according to the vendor's assessment. This demonstrates the importance of proper security configuration and the principle of defense in depth in protecting enterprise monitoring infrastructure from targeted attacks that could compromise the entire security operations ecosystem.