# CVE-2026-100891: Trusted Domain Project OpenDMARC encoding error in policy query

Source: https://junglewise.ai/threats/cve-2026-100891-a-vulnerability-has-been-found-in-trusted-domain-project  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-28. Updated: 2026-09-28  
License: CC BY 4.0 with a link back

CVE-2026-100891 · Severity: high · CVSS 7.3 · Published 2026-09-28

OpenDMARC is a library used to validate DMARC email authentication policies. A vulnerability in the policy query function can be exploited remotely to cause an encoding error, potentially disrupting email authentication and validation. The vendor has not responded to disclosure attempts, leaving systems at risk.

Technologies: [Trusted Domain Project OpenDMARC](https://junglewise.ai/threats/technologies/opendmarc). Vendors: [Trusted Domain Project](https://junglewise.ai/threats/vendors/trusted-domain-project).

## Quick answers

**Is CVE-2026-100891 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-100891 being exploited in the wild.

**How severe is CVE-2026-100891?** High severity, with a CVSS score of 7.3, published 28 September 2026.

**Which products and versions are affected?** Trusted Domain Project OpenDMARC up to 1.4.2.

**Is there a fix for CVE-2026-100891?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-100891 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-100891?** Check whether you run Trusted Domain Project OpenDMARC at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability exists in the opendmarc_policy_query_dmarc function within libopendmarc/opendmarc_policy.c, specifically in the Internationalized Domain Name Handler component. An encoding error in this function allows remote attackers to trigger the vulnerability without authentication or user interaction, potentially leading to policy validation bypass or service disruption. No vendor patch is available at this time.

## Affected products

- Trusted Domain Project OpenDMARC up to 1.4.2

## Timeline

- 2026-09-28: disclosed
- other: Vendor did not respond to early disclosure

## References

- [https://vuldb.com/cve/CVE-2026-100891](https://vuldb.com/cve/CVE-2026-100891)
- [https://vuldb.com/submit/917215](https://vuldb.com/submit/917215)

## Related threats

- [OpenDMARC improper authentication in SPF macro handler](https://junglewise.ai/threats/cve-2026-101281-a-flaw-has-been-found-in-trusted-domain-project-opendmarc-up-to)
- [Trusted Domain Project OpenDMARC authentication bypass in Multi-Record Set Handler](https://junglewise.ai/threats/cve-2026-101280-a-vulnerability-was-detected-in-trusted-domain-project-opendmarc)
- [Trusted Domain Project OpenDMARC integer overflow in DMARC parser](https://junglewise.ai/threats/cve-2026-101279-a-security-vulnerability-has-been-detected-in-trusted-domain)
- [Trusted Domain Project OpenDMARC origin validation error in PSL Wildcard Handler](https://junglewise.ai/threats/cve-2026-101278-a-weakness-has-been-identified-in-trusted-domain-project)
- [Trusted Domain Project OpenDMARC exception handling in strcasecmp](https://junglewise.ai/threats/cve-2026-101017-a-vulnerability-was-found-in-trusted-domain-project-opendmarc-up)