CVE-2021-25831
9.8
CRITICAL · CVSS 3.1 · EPSS 11.5% (pctl 96)
Patch early
EPSS 11.5% — above the 10% action threshold.
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.
Scoring
| CVSS | 9.8 (CRITICAL, v3.1) |
|---|---|
| Vector | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H |
| EPSS | 11.5% — more likely to be exploited than 96% of all CVEs |
| On CISA KEV | no |
| Public exploit | none known |
| Published | 2021-03-01 |
| Last modified | 2026-06-17 |
Affected (1)
| Vendor | Product |
|---|---|
| onlyoffice | document server |
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
- 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
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