CVE-2021-25831

Name: CVE-2021-25831
Creator: NVD / NIST
Published: 2021-03-01T16:15:14.353+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

CRITICALCVSS 9.8/10EPSS 11.50%

Last modified Jun 17, 2026

CVE-2021-25831 is a critical-severity vulnerability rated 9.8/10 on the CVSS scale. 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. EPSS estimates a 11.50% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

9.8/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS Probability

11.50%

95.5th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Vendor	Product	Versions
Onlyoffice	Document Server	>= 4.0.0-9, <= 5.6.3

References

https://github.com/ONLYOFFICE/DocumentServerProduct
https://github.com/ONLYOFFICE/coreProduct, Vendor Advisory
https://github.com/ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/Editor/BinaryFileReaderWriter.cpp#L1918Vendor Advisory
https://github.com/ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/Editor/BinaryFileReaderWriter.cpp#L241Vendor Advisory
https://github.com/ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/PPTXFormat/Logic/Fills/BlipFill.cpp#L328Vendor Advisory
https://github.com/merrychap/poc_exploits/tree/master/ONLYOFFICE/CVE-2021-25831Exploit, Vendor Advisory
https://github.com/ONLYOFFICE/DocumentServerProduct
https://github.com/ONLYOFFICE/coreProduct, Vendor Advisory
https://github.com/ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/Editor/BinaryFileReaderWriter.cpp#L1918Vendor Advisory
https://github.com/ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/Editor/BinaryFileReaderWriter.cpp#L241Vendor Advisory
https://github.com/ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/PPTXFormat/Logic/Fills/BlipFill.cpp#L328Vendor Advisory
https://github.com/merrychap/poc_exploits/tree/master/ONLYOFFICE/CVE-2021-25831Exploit, Vendor Advisory

Timeline

Published: Mar 1, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-25831?

How severe is CVE-2021-25831?

CVE-2021-25831 has a CVSS score of 9.8/10 (CRITICAL severity). The EPSS model estimates a 11.50% probability of exploitation in the next 30 days.

How do I fix CVE-2021-25831?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-25831?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST