CVE-2021-25830

Name: CVE-2021-25830
Creator: NVD / NIST
Published: 2021-03-01T16:15:14.293+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

CRITICALCVSS 9.8/10EPSS 11.76%

Last modified Jun 17, 2026

CVE-2021-25830 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 v4.2.0.236-v5.6.4.13. An attacker must request the conversion of the crafted file from DOCT into DOCX format. EPSS estimates a 11.76% chance of exploitation in the next 30 days.

Description

A file extension handling issue was found in [core] module of ONLYOFFICE DocumentServer v4.2.0.236-v5.6.4.13. An attacker must request the conversion of the crafted file from DOCT into DOCX format. Using the chain of two other bugs related to improper string handling, an attacker can achieve 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

11.76%

95.5th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Vendor	Product	Versions
Onlyoffice	Document Server	>= 4.2.0.236, <= 5.6.4.13

References

https://github.com/ONLYOFFICE/DocumentServerProduct
https://github.com/ONLYOFFICE/coreProduct
https://github.com/ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/Editor/BinaryFileReaderWriter.cpp#L1918Third Party Advisory
https://github.com/ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/Editor/BinaryFileReaderWriter.cpp#L241Third Party Advisory
https://github.com/ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/PPTXFormat/Logic/UniFill.cpp#L343Third Party Advisory
https://github.com/merrychap/poc_exploits/tree/master/ONLYOFFICE/CVE-2021-25830Exploit, Third Party Advisory
https://github.com/ONLYOFFICE/DocumentServerProduct
https://github.com/ONLYOFFICE/coreProduct
https://github.com/ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/Editor/BinaryFileReaderWriter.cpp#L1918Third Party Advisory
https://github.com/ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/Editor/BinaryFileReaderWriter.cpp#L241Third Party Advisory
https://github.com/ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/PPTXFormat/Logic/UniFill.cpp#L343Third Party Advisory
https://github.com/merrychap/poc_exploits/tree/master/ONLYOFFICE/CVE-2021-25830Exploit, Third Party Advisory

Timeline

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

Frequently Asked Questions

What is CVE-2021-25830?

How severe is CVE-2021-25830?

CVE-2021-25830 has a CVSS score of 9.8/10 (CRITICAL severity). The EPSS model estimates a 11.76% probability of exploitation in the next 30 days.

How do I fix CVE-2021-25830?

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-2021-25830?

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

Scan your code now

Source: NVD / NIST