HOMEVULNERABILITIESCVE-2021-25833
CRITICAL

CVE-2021-25833

CWE-22Published: March 1, 2021· Updated: Jun 17, 2026

9.8
CVSS v3.1

Official 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.

NVD Source

Technical Analysis

CVE-2021-25833 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in complete confidentiality breach (data exposure), full integrity compromise (data manipulation), availability disruption (denial of service), with a CVSS base score of 9.8.

CVSS v3.1 Vector Breakdown

Exploitability
Attack VectorNetwork
Attack ComplexityLow
Privileges Req.None
User InteractionNone
ScopeUnchanged
Impact
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected Vendors & Products

onlyoffice1 product(s)
document server
Source: NVD CPE · 1 total CPE entries

Exploit & PoC Resources

NO KNOWN EXPLOITNo public exploit confirmed at this time
Exploit-DB
Offensive Security exploit database
GitHub PoC Search
Community PoC repositories
Rapid7 / Metasploit
Metasploit module search
PacketStorm
Security advisories & exploits
NVD Detail
Official NIST entry
MITRE CVE
CVE Program entry
External links open in a new tab. Always verify in a controlled environment before use.

Official Patches & Advisories

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

All References (12)

→
https://github.com/ONLYOFFICE/DocumentServerProduct · Vendor Advisory
→
https://github.com/ONLYOFFICE/serverProduct
→
https://github.com/ONLYOFFICE/server/blob/v5.6.0.21/DocService/sources/converterservice.js#L200Third Party Advisory
→
https://github.com/ONLYOFFICE/server/blob/v5.6.0.21/FileConverter/sources/converter.js#L283Third Party Advisory
→
https://github.com/ONLYOFFICE/server/blob/v5.6.0.21/FileConverter/sources/converter.js#L593Third Party Advisory
→
https://github.com/merrychap/poc_exploits/tree/master/ONLYOFFICE/CVE-2021-25833Exploit · Third Party Advisory
→
https://github.com/ONLYOFFICE/DocumentServerProduct · Vendor Advisory
→
https://github.com/ONLYOFFICE/serverProduct
→
https://github.com/ONLYOFFICE/server/blob/v5.6.0.21/DocService/sources/converterservice.js#L200Third Party Advisory
→
https://github.com/ONLYOFFICE/server/blob/v5.6.0.21/FileConverter/sources/converter.js#L283Third Party Advisory
→
https://github.com/ONLYOFFICE/server/blob/v5.6.0.21/FileConverter/sources/converter.js#L593Third Party Advisory
→
https://github.com/merrychap/poc_exploits/tree/master/ONLYOFFICE/CVE-2021-25833Exploit · Third Party Advisory

Quick Facts

CVE IDCVE-2021-25833
CVSS Score9.8 / 10
SeverityCRITICAL
WeaknessCWE-22
CISA KEVNo
Affected1 vendor(s)
PublishedMar 1, 2021

Related CVEs (CWE-22)

CVE-2014-7985
10.0
CVE-2014-0598
10.0
CVE-2014-2863
10.0
CVE-2014-0754
10.0
CVE-2014-2864
10.0
CVE-2014-9373
10.0

Recommended Actions

  • →Apply vendor patches immediately
  • →Monitor CVE-2021-25833 in threat intel feeds
  • →Review IDS/IPS signatures for exploitation attempts
Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWATCH.COM. CVE data is provided under the NVD usage policy.
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