What’s Vulnerable › Vulnerabilities

CVE-2021-25833

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 43.5% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2021-03-01 · updated 2026-06-17
• Weakness: CWE-22

Description

A file extension handling issue was found in [server] module of ONLYOFFICE DocumentServer v4.2.0.71-v5.6.0.21. The file extension is controlled by an attacker through the request data and leads to arbitrary file overwriting. Using this vulnerability, a remote attacker can obtain remote code execution on DocumentServer.

Affected products

• ONLYOFFICE Document Server: from 4.2.0.71 through 5.6.0.21

References

• https://github.com/ONLYOFFICE/DocumentServer
• https://github.com/ONLYOFFICE/server
• https://github.com/ONLYOFFICE/server/blob/v5.6.0.21/DocService/sources/converterservice.js#L200
• https://github.com/ONLYOFFICE/server/blob/v5.6.0.21/FileConverter/sources/converter.js#L283
• https://github.com/ONLYOFFICE/server/blob/v5.6.0.21/FileConverter/sources/converter.js#L593
• https://github.com/merrychap/poc_exploits/tree/master/ONLYOFFICE/CVE-2021-25833
• https://github.com/ONLYOFFICE/DocumentServer
• https://github.com/ONLYOFFICE/server
• https://github.com/ONLYOFFICE/server/blob/v5.6.0.21/DocService/sources/converterservice.js#L200
• https://github.com/ONLYOFFICE/server/blob/v5.6.0.21/FileConverter/sources/converter.js#L283
• https://github.com/ONLYOFFICE/server/blob/v5.6.0.21/FileConverter/sources/converter.js#L593
• https://github.com/merrychap/poc_exploits/tree/master/ONLYOFFICE/CVE-2021-25833

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