{"id":"CVE-2021-25833","url":"https://www.cyber-defence.io/tools/cve/CVE-2021-25833","generatedAt":"2026-11-05T01:39:13.098Z","title":"The file extension is controlled by an attacker through the request data and leads to arbitrary file overwriting.","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.","published":"2021-03-01T16:15:15.000Z","lastModified":"2026-06-17T03:42:30.000Z","status":"Modified","sourceIdentifier":"cve@mitre.org","cvss":{"version":"3.1","score":9.8,"severity":"CRITICAL","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"},"cwe":["CWE-22"],"affected":["onlyoffice/document server"],"epss":{"score":0.43534,"percentile":0.98742,"date":"2026-11-03","history":[]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"urgent","text":"EPSS puts the probability of exploitation in the next 30 days at 43.5%, higher than 99% of all known CVEs. Patch or mitigate before the next change window."},"changes":[],"references":[{"url":"https://github.com/ONLYOFFICE/DocumentServer","tags":["Product","Vendor Advisory"],"source":"cve@mitre.org"},{"url":"https://github.com/ONLYOFFICE/server","tags":["Product"],"source":"cve@mitre.org"},{"url":"https://github.com/ONLYOFFICE/server/blob/v5.6.0.21/DocService/sources/converterservice.js#L200","tags":["Third Party Advisory"],"source":"cve@mitre.org"},{"url":"https://github.com/ONLYOFFICE/server/blob/v5.6.0.21/FileConverter/sources/converter.js#L283","tags":["Third Party Advisory"],"source":"cve@mitre.org"},{"url":"https://github.com/ONLYOFFICE/server/blob/v5.6.0.21/FileConverter/sources/converter.js#L593","tags":["Third Party Advisory"],"source":"cve@mitre.org"},{"url":"https://github.com/merrychap/poc_exploits/tree/master/ONLYOFFICE/CVE-2021-25833","tags":["Exploit","Third Party Advisory"],"source":"cve@mitre.org"},{"url":"https://github.com/ONLYOFFICE/DocumentServer","tags":["Product","Vendor Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://github.com/ONLYOFFICE/server","tags":["Product"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://github.com/ONLYOFFICE/server/blob/v5.6.0.21/DocService/sources/converterservice.js#L200","tags":["Third Party Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://github.com/ONLYOFFICE/server/blob/v5.6.0.21/FileConverter/sources/converter.js#L283","tags":["Third Party Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://github.com/ONLYOFFICE/server/blob/v5.6.0.21/FileConverter/sources/converter.js#L593","tags":["Third Party Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://github.com/merrychap/poc_exploits/tree/master/ONLYOFFICE/CVE-2021-25833","tags":["Exploit","Third Party Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2021-25833","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}