Critical severity9.8NVD Advisory· Published Mar 1, 2021· Updated Jun 17, 2026
CVE-2021-25831
CVE-2021-25831
Description
A file extension handling issue was found in [core] module of ONLYOFFICE DocumentServer v4.0.0-9-v5.6.3. An attacker must request the conversion of the crafted file from PPTT into PPTX format. Using the chain of two other bugs related to improper string handling, a remote attacker can obtain remote code execution on DocumentServer.
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Affected products
3- cpe:2.3:a:onlyoffice:document_server:*:*:*:*:*:*:*:*Range: >=4.0.0-9,<=5.6.3
- ONLYOFFICE/DocumentServerdescription
- Range: v4.0.0-9-v5.6.3
Patches
Vulnerability mechanics
References
4- github.com/merrychap/poc_exploits/tree/master/ONLYOFFICE/CVE-2021-25831nvdExploitVendor Advisory
- github.com/ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/Editor/BinaryFileReaderWriter.cppnvdVendor Advisory
- github.com/ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/Editor/BinaryFileReaderWriter.cppnvdVendor Advisory
- github.com/ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/PPTXFormat/Logic/Fills/BlipFill.cppnvdVendor Advisory
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