CVE-2021-25831
CVE-2021-25831 is a critical-severity vulnerability in Onlyoffice Document Server with a CVSS 3.x base score of 9.8. Its EPSS exploit-prediction score of 12% places it in the 96th percentile, indicating an elevated likelihood of exploitation.
Key facts
- Severity: Critical (CVSS 3.x base score 9.8)
- CVSS v2: 7.5
- EPSS exploit prediction: 12% (96th percentile)
- Actively exploited: Not listed in CISA KEV
- Affected product: Onlyoffice Document Server
- Published:
- Last modified:
Description
A file extension handling issue was found in [core] module of ONLYOFFICE DocumentServer v4.0.0-9-v5.6.3. An attacker must request the conversion of the crafted file from PPTT into PPTX format. Using the chain of two other bugs related to improper string handling, a remote attacker can obtain remote code execution on DocumentServer.
Frequently asked questions
- What is CVE-2021-25831?
- A file extension handling issue was found in [core] module of ONLYOFFICE DocumentServer v4.0.0-9-v5.6.3. An attacker must request the conversion of the crafted file from PPTT into PPTX format. Using the chain of two other bugs related to improper string handling, a remote attacker can obtain remote code execution on DocumentServer.
- How severe is CVE-2021-25831?
- CVE-2021-25831 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
- Is CVE-2021-25831 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 12% (96th percentile), an estimate of the probability of exploitation in the next 30 days.
- What products are affected by CVE-2021-25831?
- CVE-2021-25831 affects Onlyoffice Document Server. See the affected-products list for the exact vulnerable versions.
- How do I fix CVE-2021-25831?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
- When was CVE-2021-25831 published?
- CVE-2021-25831 was published on 2021-03-01 and last updated on 2026-06-17.
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/Fills/BlipFill.cpp#L328
- https://github.com/merrychap/poc_exploits/tree/master/ONLYOFFICE/CVE-2021-25831
Affected products (1)
- cpe:2.3:a:onlyoffice:document_server:*:*:*:*:*:*:*:*
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