CVE-2026-101014 in OpenDMARC
Summary
by MITRE • 09/28/2026
A vulnerability was detected in Trusted Domain Project OpenDMARC up to 1.4.2. Affected by this vulnerability is the function opendmarc_util_cleanup in the library libopendmarc/opendmarc_util.c of the component DMARC Record Parser. Performing a manipulation results in off-by-one. The attack may be initiated remotely. The exploit is now public and may be used. The patch is named b3b1da9264bc80324094a27c71e7369bdedc62ae. To fix this issue, it is recommended to deploy a patch.
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Analysis
by VulDB Data Team • 09/28/2026
The Trusted Domain Project OpenDMARC software, specifically versions up through 1.4.2, contains a critical memory safety vulnerability within its DMARC record parsing functionality. This flaw resides in the opendmarc_util_cleanup function located in the libopdmarc/opendmrc_util.c source file. The component is responsible for processing Domain-based Message Authentication, Reporting, and Conformance records, which are essential for email security infrastructure. When this module processes malformed or specifically crafted input data, it triggers an off-by-one error during memory management operations. This type of vulnerability typically arises when a loop boundary condition or buffer index calculation fails to account for the null terminator in C-style strings or mismanages array indices by exactly one unit. Such errors can lead to writing beyond the allocated bounds of a heap-allocated buffer, potentially corrupting adjacent memory structures and leading to unpredictable application behavior.
From a technical perspective, this off-by-one error falls under CWE-193, which describes an Off-by-One Error in memory operations. The vulnerability allows for potential out-of-bounds write access, which is categorized as CWE-787: Out-of-Bounds Write. In the context of C/C++ applications like OpenDMARC, heap-based buffer overflows are particularly dangerous because they can overwrite metadata associated with adjacent heap chunks or corrupt function pointers stored in nearby memory regions. An attacker who can control the input data processed by this parser could potentially leverage this flaw to execute arbitrary code on the affected system. The ability to manipulate memory layout and inject shellcode makes this a high-severity issue, especially given that OpenDMARC often runs with elevated privileges or as part of critical mail server infrastructure where availability and integrity are paramount.
The operational impact of this vulnerability is significant due to its remote exploitability. Since the flaw exists in the DMARC record parser, an attacker can initiate the attack remotely by sending specially crafted email messages containing maliciously formatted DMARC tags to a system running the vulnerable version of OpenDMARC. The fact that public exploits are available further exacerbates the risk landscape, as it lowers the barrier for entry for less sophisticated threat actors who may not possess advanced reverse engineering skills but can utilize existing proof-of-concept code to compromise target systems. Successful exploitation could result in complete system takeover, allowing attackers to intercept or modify email traffic, exfiltrate sensitive data, or use the compromised server as a pivot point for further network intrusion. This aligns with MITRE ATT&CK techniques related to initial access and privilege escalation, specifically those involving software vulnerabilities that allow remote code execution.
To mitigate this risk, organizations running OpenDMARC must immediately apply the patch identified by commit hash b3b1da9264bc80324094a27c71e7369bdedc62ae. This update corrects the boundary condition in the opendmarc_util_cleanup function, ensuring that memory operations remain within allocated limits and preventing the off-by-one write from occurring. Administrators should verify their current version of OpenDMARC against this patch level before deployment. In addition to applying the software fix, it is advisable to implement network-level controls such as ingress filtering or web application firewalls that can detect and block anomalous email traffic patterns associated with exploitation attempts. Regular vulnerability scanning and monitoring for new CVEs related to mail server components are also recommended practices to maintain a robust security posture against evolving threats targeting infrastructure services.