Date: Wed, 11 Sep 2019 12:43:19 +0200 From: Hanno Böck <hanno@...eck.de> To: oss-security@...ts.openwall.com Subject: OpenDMARC signature bypass with multiple From addresses Hi, Protonmail reported about a phishing incident in July: https://protonmail.com/blog/bellingcat-cyberattack-phishing/ This had this somewhat mysterious chapter: "Furthermore, the attackers attempted to exploit an unpatched vulnerability in an open source software that is widely used by email providers in an effort to bypass spam and abuse filters. We were previously aware of this vulnerability and have already been watching it for some time, but we will not disclose it here because the software in question is not developed by ProtonMail, and it has not yet been patched by the software maintainers. This vulnerability, however, is not widely known and indicates a higher level of sophistication on the part of the attackers." After asking protonmail multiple times for a statement they answered and I learned that it's about this issue in OpenDMARC: https://github.com/trusteddomainproject/OpenDMARC/pull/48 It's an issue where by specifying multiple From addresses only one of them gets DMARC-checked. There's no reaction from the OpenDMARC developers and it's unclear whether it's still actively developed. Given this is already actively exploited I think people should be aware of it and distros should probably apply the patch from the PR. -- Hanno Böck https://hboeck.de/ mail/jabber: hanno@...eck.de GPG: FE73757FA60E4E21B937579FA5880072BBB51E42
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