Improper Certificate Validation issue in LibreOffice and OpenOffice allows signed docs spoofing

Pierluigi Paganini October 11, 2021

LibreOffice and OpenOffice released security updates to address a vulnerability that can be exploited by an attacker to spoof signed documents. 

LibreOffice and OpenOffice released security updates to address a moderate-severity flaw that can allow attackers to manipulate documents to appear as signed by a trusted source. 

“It is possible for an attacker to manipulate documents to appear to be signed by a trusted source. All versions of Apache OpenOffice up to 4.1.10 are affected.” reads the advisory for this vulnerability.

The flaw has been addressed with the release of version 4.1.1. The flaw was reported by Simon Rohlmann, Vladislav Mladenov, Christian Mainka, and Jorg Schwenk of Ruhr University Bochum, Germany.

In a real attack scenario, threat actors can sign weaponized documents to make them appear as created by a trusted source.

Experts pointed out that the CVE-2021-25635 flaw also affects LibreOffice that tracked the vulnerability as CVE-2021-25635. 

“An Improper Certificate Validation vulnerability in LibreOffice allowed an attacker to self sign an ODF document, with a signature untrusted by the target, then modify it to change the signature algorithm to an invalid (or unknown to LibreOffice) algorithm and LibreOffice would incorrectly present such a signature with an unknown algorithm as a valid signature issued by a trusted person.” reads the advisory published by LibreOffice.

Libre Office addressed the issue with the release 7.0.5 or 7.1.1 and later. 

Users that are not able to update their installs to the latest version should disable the macro features.

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Pierluigi Paganini

(SecurityAffairs – hacking, OpenOffice)

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