OpenDMARC Input Validation Flaw Enables Domain Spoofing

A flaw has been found in Trusted Domain Project OpenDMARC up to 1.4.2. Affected by this issue is some unknown functionality of the file policy.c of the component Domain Handler. Executing a manipulation can lead to improper validation of unsafe equivalence in input. The attack may be launched remotely. The exploit has been published and may be used. The vendor was contacted early about this disclosure but did not respond in any way.

Casky was already ahead

This CVE exploits attack patterns that Casky's 323matched skills already investigate — long before this vulnerability was disclosed. Claude's reasoning model maps these techniques to MITRE ATT&CK, so practitioners who ran these skills have already seen the threat behaviour in their findings.

Analysis

OpenDMARC versions up to 1.4.2 contain a critical input validation vulnerability in the policy.c Domain Handler that fails to properly validate domain equivalence checks. This flaw allows attackers to bypass DMARC authentication mechanisms through manipulated input, potentially enabling email spoofing and domain impersonation attacks. Organizations deploying OpenDMARC for email authentication and spam filtering are directly affected, particularly those relying on it as a primary defense against phishing and business email compromise (BEC) attacks. The vulnerability's remote exploitability and published exploit details significantly increase the risk profile for unpatched deployments.

Casky's 323 mapped security skills leverage Claude's extended reasoning to detect attack patterns associated with TA0001 (Initial Access) and TA0043 (Reconnaissance) techniques, identifying how threat actors probe and exploit DMARC validation weaknesses. Practitioners using Casky would observe findings related to anomalous domain authentication requests, suspicious equivalence mappings in email headers, and policy bypass attempts in their DMARC logs and traffic analysis. The platform's skills help correlate CWE-20 (improper input validation) and CWE-1289 (unsafe equivalence comparisons) with observable indicators—such as emails claiming to be from trusted domains that fail proper validation checks—enabling security teams to distinguish between legitimate authentication failures and active exploitation attempts before they reach user inboxes.

Live Threat IntelligenceComing soon

Casky Risk Score

—

EPSS Probability

—

Shodan Exposure

—

GreyNoise Signal

—

Composite risk scoring from EPSS, CISA KEV, Shodan, and GreyNoise — 21 security APIs correlated into a single Casky Risk Score. Coming in Casky Pro. Join early access →

323 Casky skills cover this attack pattern

These skills use Claude AI's reasoning model to surface findings in the same attack categories as CVE-2026-101015.

Abuse of Public-Facing API: Mobile API Abuse

mobile security · low

Run

abusing-dpapi-for-credential-access

red teaming · high

Run

abusing-shadow-credentials-for-privesc

red teaming · high

Run

MITRE ATT&CK Techniques

TA0001 TA0043

Investigate the attack patterns behind CVE-2026-101015

Casky has 323 skills that investigate the attack patterns behind CVE-2026-101015. Run one and get CVSS-scored findings in 3 minutes.

Run the skill that detects this →

X Instagram LinkedIn