Title: Content Manipulation with Double Certificate Attack
Announced: October 11, 2021
Fixed in: LibreOffice 7.0.6/7.1.2
LibreOffice supports digital signatures of ODF documents and macros within documents, presenting visual aids that no alteration of the document occurred since the last signing and that the signature is valid.
An Improper Certificate Validation vulnerability in LibreOffice allowed an attacker to create a digitally signed ODF document, by manipulating the documentsignatures.xml or macrosignatures.xml stream within the document to combine multiple certificate data, which when opened caused LibreOffice to display a validly signed indicator but whose content was unrelated to the signature shown.
NDS of Ruhr University Bochum for discovering and reporting this problem.
Thanks to Michael Stahl of allotropia software GmbH for solving this problem.