CVE-2021-21439 in Community Edition
Summary
by MITRE • 06/14/2021
DoS attack can be performed when an email contains specially designed URL in the body. It can lead to the high CPU usage and cause low quality of service, or in extreme case bring the system to a halt. This issue affects: OTRS AG ((OTRS)) Community Edition 6.0.x version 6.0.1 and later versions. OTRS AG OTRS 7.0.x version 7.0.26 and prior versions; 8.0.x version 8.0.13 and prior versions.
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Analysis
by VulDB Data Team • 06/18/2021
The vulnerability identified as CVE-2021-21439 represents a denial of service weakness within the OTRS Community Edition email management system that can be exploited through crafted URL content within email messages. This flaw specifically targets versions 6.0.1 and later of the 6.0.x release line, as well as prior versions of the 7.0.x and 8.0.x branches up to 7.0.26 and 8.0.13 respectively. The vulnerability stems from insufficient input validation and sanitization of URLs contained within email bodies, creating a pathway for malicious actors to craft specially designed hyperlinks that trigger excessive system resource consumption.
The technical exploitation of this vulnerability occurs when the OTRS system processes incoming email messages containing maliciously constructed URLs. The system's parsing mechanism fails to adequately validate or limit the processing of these URLs, leading to recursive or excessive computational operations that consume disproportionate amounts of cpu cycles. This occurs because the application does not implement proper bounds checking or resource limiting when handling URL resolution and processing within email content. The vulnerability manifests as high cpu utilization rates that can degrade system performance significantly, potentially leading to complete service unavailability under extreme conditions.
From an operational perspective, this vulnerability poses substantial risk to organizations relying on OTRS for their email management and customer service operations. The denial of service condition can result in degraded quality of service where legitimate email processing becomes severely impacted, affecting customer support workflows and business operations. In extreme scenarios, the excessive cpu consumption can cause complete system hangs or crashes, effectively rendering the email management system unusable. The impact is particularly concerning given that OTRS is widely used in enterprise environments where continuous availability of customer service systems is critical for business operations and customer satisfaction.
The vulnerability aligns with CWE-400, which describes "Uncontrolled Resource Consumption" as a weakness that occurs when an application fails to properly manage resource usage, leading to resource exhaustion. This weakness is often exploited through input manipulation techniques where attackers craft specific inputs that cause the application to consume excessive computational resources. From an attack framework perspective, this vulnerability can be categorized under the ATT&CK technique T1499.004, which covers "Toggle System Audit Logging" and related denial of service methods that consume system resources to disrupt service availability. Organizations should implement immediate mitigations including input validation controls, URL sanitization mechanisms, and resource consumption monitoring to prevent exploitation. The recommended approach involves patching affected systems to the latest available versions of OTRS, implementing email content filtering rules that block suspicious URL patterns, and establishing monitoring alerts for unusual cpu usage patterns that could indicate exploitation attempts.