CVE-2026-101279 in OpenDMARC
Summary
by MITRE • 09/29/2026
A security vulnerability has been detected in Trusted Domain Project OpenDMARC up to 1.4.2. This impacts an unknown function of the file libopendmarc/opendmarc_policy.c of the component DMARC Parser. The manipulation of the argument pct leads to integer overflow. Remote exploitation of the attack is possible. The exploit has been disclosed publicly and may be used. The vendor was contacted early about this disclosure but did not respond in any way.
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Analysis
by VulDB Data Team • 09/29/2026
The Trusted Domain Project OpenDMARC software, specifically versions up through 1.4.2, contains a critical security vulnerability within its DMARC parsing component that allows for remote code execution or denial of service via integer overflow conditions. This flaw resides deep within the core logic responsible for processing policy reports and directives received from external domains. The specific point of failure is located in the libopendmarc/opendmarc_policy.c source file, where a function handling the percentage argument associated with DMARC policies fails to properly validate input boundaries before performing arithmetic operations. This lack of rigorous boundary checking creates an environment ripe for exploitation by malicious actors who can craft specially crafted network packets or email headers containing malformed data designed to trigger this overflow condition during the parsing phase.
The technical nature of this vulnerability centers on improper handling of integer values, specifically classified under Common Weakness Enumeration as CWE-190 Integer Overflow or Wraparound. When an attacker supplies a value for the pct argument that exceeds the expected range or is crafted in a way to cause arithmetic wrap-around during internal calculations, the resulting memory allocation or buffer management may become inconsistent with the actual data size required. This discrepancy can lead to heap corruption, stack-based buffer overflows, or other memory safety violations depending on how the underlying C library handles the miscalculated sizes. Because OpenDMARC operates as a daemon that processes incoming email traffic in real-time, this vulnerability is directly exploitable by remote attackers without requiring any form of authentication, making it particularly dangerous for mail servers and infrastructure providers relying on DMARC validation to secure their domains against spoofing attacks.
The operational impact of exploiting this integer overflow can be severe, ranging from complete service disruption to unauthorized code execution on the host system. If an attacker successfully triggers a buffer overflow through the malformed pct argument, they may achieve arbitrary read or write access to memory regions associated with the OpenDMARC process. This could allow for the exfiltration of sensitive configuration data, such as private keys used for signing DMARC reports, or potentially lead to full compromise of the mail server if combined with other vulnerabilities in the surrounding system stack. Furthermore, even without achieving code execution, a successful exploitation attempt can cause the OpenDMARC daemon to crash repeatedly, leading to a denial-of-service condition that disrupts email delivery and validation services for all users relying on that infrastructure. The fact that proof-of-concept exploits have been publicly disclosed significantly lowers the barrier to entry for attackers, increasing the likelihood of automated scanning and targeted attacks against exposed instances.
Industry frameworks such as MITRE ATT&CK categorize this type of vulnerability under techniques related to initial access or execution via exploited vulnerabilities in network services. Specifically, it aligns with T1190 Exploit Public-Facing Application, where adversaries leverage known flaws in internet-facing software to gain a foothold within the target environment. The absence of vendor response despite early notification highlights a critical gap in supply chain security and incident management practices for open-source projects maintained by smaller teams or independent contributors. Organizations currently running OpenDMARC versions prior to 1.4.3 are strongly advised to upgrade immediately upon release, as this update is expected to contain the necessary patches to validate input parameters correctly and prevent integer overflows during policy parsing. In the interim, network-level mitigations such as strict rate limiting on incoming SMTP connections or deep packet inspection rules that detect anomalous header sizes can help reduce the attack surface until a permanent fix is deployed.