| Title | The Trusted Domain Project OpenDMARC 1.4.2 Improper Authentication |
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| Description | OpenDMARC 1.4.2 incorrectly rejects an entire DMARC record when an optional reporting-related tag contains an invalid value. Although malformed optional tags should be ignored after the required DMARC fields have been successfully parsed, OpenDMARC returns `dmarc=permerror` for the complete record.
As a result, a valid `p=reject` or `p=quarantine` policy may not be enforced when the record contains an invalid optional value, such as `fo=9`. A remote unauthenticated attacker can exploit this condition by sending forged messages from an affected domain, which may be treated as having no enforceable DMARC policy.
The issue can also be triggered deliberately by an attacker who is able to modify or influence the affected DMARC record, including through delegated DNS administration. Successful exploitation may allow forged messages to bypass the domain’s intended DMARC policy. |
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| Source | ⚠️ https://xuyongzhe-vt.github.io/share/opendmarc-bad-tag-drops-policy.html |
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| User | yongzhe_xu (UID 100420) |
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| Submission | 08/07/2026 04:15 (2 months ago) |
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| Moderation | 09/27/2026 13:33 (2 months later) |
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| Status | Accepted |
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| VulDB entry | 410886 [Trusted Domain Project OpenDMARC up to 1.4.2 opendmarc_policy.c opendmarc_policy_parse_dmarc fo/rf/ri/pct/sp/adkim/aspf/rua/ruf exceptional condition] |
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| Points | 20 |
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