CVE-2021-36093 in Community Edition
Summary
by MITRE • 09/06/2021
It's possible to create an email which can be stuck while being processed by PostMaster filters, causing DoS. 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 7.0.28 and prior versions; 8.0.x version 8.0.15 and prior versions.
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Analysis
by VulDB Data Team • 09/09/2021
This vulnerability represents a denial of service condition within the OTRS Community Edition email processing system that can be exploited through carefully crafted email messages. The issue specifically impacts the PostMaster filtering mechanisms that are responsible for handling incoming email traffic and applying various processing rules to determine how messages should be routed or handled within the system. The flaw allows an attacker to construct email content that causes the filtering process to become indefinitely stuck, effectively preventing legitimate email processing and creating a service disruption scenario that can impact the availability of the entire email handling infrastructure.
The technical root cause of this vulnerability lies in insufficient input validation and processing logic within the PostMaster filter components. When the system encounters specially crafted email messages, the filtering algorithms fail to properly handle certain content patterns or structures, leading to infinite loops or resource exhaustion during the processing phase. This behavior is particularly concerning because email filtering is a critical component of the system's core functionality, and any disruption to this process affects the entire email handling workflow. The vulnerability affects multiple versions of the OTRS platform including the 6.0.x series starting from version 6.0.1, as well as the 7.0.x series up to version 7.0.28 and the 8.0.x series up to version 8.0.15, indicating this represents a widespread issue across the platform's lifecycle.
The operational impact of this vulnerability extends beyond simple service disruption to potentially create cascading effects within email processing workflows. When the PostMaster filters become stuck, they consume system resources and prevent other legitimate emails from being processed, effectively creating a denial of service condition that can impact business operations. This vulnerability is particularly dangerous in environments where email is a critical communication channel, as it can render the entire email handling system unusable. The attack vector is relatively simple to execute since it only requires the ability to send specially crafted emails to the affected system, making it accessible to attackers with minimal technical expertise. Organizations using OTRS Community Edition are particularly vulnerable as this affects the core email processing functionality that is essential for ticket management and customer communication workflows.
Organizations should implement immediate mitigations including applying the vendor-provided patches or updates that address this specific filtering logic issue. The recommended approach involves upgrading to versions that contain the security fixes, as these releases include enhanced input validation and improved processing error handling that prevent the infinite loop conditions. Network-level mitigations such as email content filtering at the perimeter can also help reduce the impact by blocking suspicious email patterns before they reach the vulnerable system components. Additionally, implementing monitoring and alerting for unusual processing behavior can help detect when the filters are becoming stuck, allowing for faster response times. From a security framework perspective, this vulnerability aligns with CWE-400 which covers unspecified errors in resource management, and it maps to ATT&CK technique T1499.004 related to network denial of service attacks. The vulnerability demonstrates the importance of proper input validation and error handling in security-critical components, particularly those involved in processing untrusted data from external sources.