CVE-2021-25831
An attacker must request the conversion of the crafted file from PPTT into PPTX format.
Does this matter?
EPSS puts the probability of exploitation in the next 30 days at 11.5%, higher than 96% of all known CVEs. Patch or mitigate before the next change window.
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.
- CVSS 3.1
- 9.8 CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- EPSS
- 11.50% probability · 96th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Not listed
- Affected
- onlyoffice/document server
- Source
- cve@mitre.org
EPSS 11.5% since 3 November 2026; no change recorded yet. The dashed line is the ten per cent mark our analysts treat as “patch before the next change window”. Points are recorded when the score first appears and whenever it moves by a percentage point or more.
References
- https://github.com/ONLYOFFICE/DocumentServerProduct
- https://github.com/ONLYOFFICE/coreProduct, Vendor Advisory
- https://github.com/ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/Editor/BinaryFileReaderWriter.cpp#L1918Vendor Advisory
- https://github.com/ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/Editor/BinaryFileReaderWriter.cpp#L241Vendor Advisory
- https://github.com/ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/PPTXFormat/Logic/Fills/BlipFill.cpp#L328Vendor Advisory
- https://github.com/merrychap/poc_exploits/tree/master/ONLYOFFICE/CVE-2021-25831Exploit, Vendor Advisory
- https://github.com/ONLYOFFICE/DocumentServerProduct
- https://github.com/ONLYOFFICE/coreProduct, Vendor Advisory
- https://github.com/ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/Editor/BinaryFileReaderWriter.cpp#L1918Vendor Advisory
- https://github.com/ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/Editor/BinaryFileReaderWriter.cpp#L241Vendor Advisory
- https://github.com/ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/PPTXFormat/Logic/Fills/BlipFill.cpp#L328Vendor Advisory
- https://github.com/merrychap/poc_exploits/tree/master/ONLYOFFICE/CVE-2021-25831Exploit, Vendor Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.