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Fencer Vulns
critical 9.8

CVE-2021-25831 in the critical feed json

A file extension handling issue was found in [core] module of ONLYOFFICE DocumentServer v4.0.0-9-v5.6.3.

published 2021-03-01 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-12714

cvss
9.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
11.5%
EPSS 11.5% chance of exploitation in 30 days, percentile 96%
public exploits
0
none known

Summary

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.

Exploit prediction

11.50% chance of exploitation in the next 30 days, higher than 96% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/merrychap/poc_exploits/tree/master/ONLYOFFICE/CVE-2021-25831 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 7.5 AV:N/AC:L/Au:N/C:P/I:P/A:P

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.