CVE-2021-34555 in OpenDMARC
Summary
by MITRE • 06/10/2021
OpenDMARC 1.4.1 and 1.4.1.1 allows remote attackers to cause a denial of service (NULL pointer dereference and application crash) via a multi-value From header field.
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Analysis
by VulDB Data Team • 06/13/2021
The vulnerability identified as CVE-2021-34555 affects OpenDMARC versions 1.4.1 and 1.4.1.1, representing a critical denial of service weakness that can be exploited by remote attackers to crash the application. This flaw specifically manifests when the system processes email messages containing multi-value From header fields, which are legitimate email formatting constructs that can contain multiple sender addresses within a single header. The vulnerability stems from inadequate input validation within the DMARC processing logic, where the software fails to properly handle scenarios involving multiple values in the From header field. When such malformed input is encountered, the application attempts to dereference a null pointer during its processing routine, leading to an immediate application crash and subsequent denial of service for legitimate email processing requests.
The technical implementation of this vulnerability aligns with CWE-476, which describes null pointer dereference conditions in software systems. This weakness occurs because the OpenDMARC implementation does not adequately validate or sanitize the From header field contents before attempting to parse multiple values. The attack vector is particularly concerning as it requires no authentication or special privileges, making it accessible to any remote attacker who can send email messages to the vulnerable system. The flaw operates at the application level within the email validation and authentication processing pipeline, where the software assumes that header fields will contain single values and does not account for legitimate multi-value headers that conform to email standards. This represents a classic buffer over-read or pointer handling error that can be triggered by carefully crafted email messages containing malformed From headers with multiple addresses.
The operational impact of this vulnerability extends beyond simple service disruption as it can effectively render the email security infrastructure unusable for legitimate email traffic. Organizations relying on OpenDMARC for email authentication and DMARC policy enforcement face significant risk of email processing failures, which can result in legitimate emails being rejected or delayed while malicious actors exploit the vulnerability to disrupt services. The vulnerability affects the core email processing functionality of the system, potentially causing cascading failures in email security workflows and compromising the organization's ability to enforce email authentication policies. This weakness particularly impacts environments where email security is critical, such as enterprise email systems, government agencies, and organizations with strict email compliance requirements, where service availability is paramount for business operations and security monitoring.
Mitigation strategies for this vulnerability should include immediate patching of OpenDMARC installations to versions that address the null pointer dereference issue, as well as implementing defensive email filtering measures that can detect and block potentially malicious email headers before they reach the vulnerable processing components. Organizations should also consider implementing monitoring and alerting systems that can detect application crashes or unusual processing patterns that may indicate exploitation attempts. The solution aligns with ATT&CK technique T1499.004, which covers network denial of service attacks, and requires defensive measures such as input validation, application hardening, and proper error handling. Additionally, implementing rate limiting and email header validation at network boundaries can provide additional protection against exploitation attempts, while regular security assessments should be conducted to identify similar vulnerabilities in other email processing components within the organization's infrastructure.