What’s Vulnerable › Vulnerabilities

CVE-2021-25830

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 11.8% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2021-03-01 · updated 2026-06-17

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.

Affected products

• ONLYOFFICE Document Server: from 4.2.0.236 through 5.6.4.13

References

• https://github.com/ONLYOFFICE/DocumentServer
• https://github.com/ONLYOFFICE/core
• https://github.com/ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/Editor/BinaryFileReaderWriter.cpp#L1918
• https://github.com/ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/Editor/BinaryFileReaderWriter.cpp#L241
• https://github.com/ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/PPTXFormat/Logic/UniFill.cpp#L343
• https://github.com/merrychap/poc_exploits/tree/master/ONLYOFFICE/CVE-2021-25830
• https://github.com/ONLYOFFICE/DocumentServer
• https://github.com/ONLYOFFICE/core
• https://github.com/ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/Editor/BinaryFileReaderWriter.cpp#L1918
• https://github.com/ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/Editor/BinaryFileReaderWriter.cpp#L241
• https://github.com/ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/PPTXFormat/Logic/UniFill.cpp#L343
• https://github.com/merrychap/poc_exploits/tree/master/ONLYOFFICE/CVE-2021-25830

Get alerted when CVE-2021-25830 or the next vulnerability affects your stack