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CVE-2021-25831

35
FAUCET Score

CVE-2021-25831 is a critical remote code execution vulnerability affecting ONLYOFFICE DocumentServer versions 4.0.0-9 through 5.6.3. It stems from a file extension handling issue within the core module, which, when combined with two string handling bugs, allows an attacker to achieve RCE by requesting the conversion of a specially crafted PPTT file to PPTX format. With a CVSS score of 9.8, this vulnerability is easily exploitable over the network without user interaction, leading to complete compromise of confidentiality, integrity, and availability. There is currently no evidence of active exploitation, public exploit code (Metasploit, Nuclei, ExploitDB), or significant community discussion or media coverage surrounding this CVE.

Impacted Technologies

VendorProductVersion(s)CPE
>= 4.0.0-9, <= 5.6.3CPE matchmatch criteria
cpe:2.3:a:onlyoffice:document_server:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

9.8CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
Exploitability Score
3.9
Impact Score
5.9
CvssVersion
3.1

Exploit Intelligence

EPSS Score
11.50%
Probability of exploitation in next 30 days
EPSS Percentile
95.6%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.1150 is in the 91st percentile among its peer group of 36,862 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.3 Bluesky, 0.3 Mastodon, and 2.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.3 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Vendor Patches (1)

github_advisoryvendor investigatingvia nvd_reference
View patch

References

github.com / merrychap/poc_exploits/tree/master/ONLYOFFICE/CVE-2021-25831
ExploitVendor Advisory
github.com / ONLYOFFICE/core
ProductVendor Advisory
github.com / ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/Editor/BinaryFileReaderWriter.cpp
Vendor Advisory
github.com / ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/Editor/BinaryFileReaderWriter.cpp
Vendor Advisory
github.com / ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/PPTXFormat/Logic/Fills/BlipFill.cpp
Vendor Advisory
github.com / ONLYOFFICE/DocumentServer
Product