How severe is CVE-2021-25833?

CVE-2021-25833 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-2021-25833 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 44% (99th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-25833?

CVE-2021-25833 affects Onlyoffice Document Server. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-25833?

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-2021-25833 published?

CVE-2021-25833 was published on 2021-03-01 and last updated on 2026-06-17.

CVE-2021-25833

CVE-2021-25833 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 44% places it in the 99th percentile, indicating an elevated likelihood of exploitation. The underlying weakness is classified as CWE-22.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 7.5
EPSS exploit prediction: 44% (99th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-22
Affected product: Onlyoffice Document Server
Published: 2021-03-01
Last modified: 2026-06-17

Description

A file extension handling issue was found in [server] module of ONLYOFFICE DocumentServer v4.2.0.71-v5.6.0.21. The file extension is controlled by an attacker through the request data and leads to arbitrary file overwriting. Using this vulnerability, a remote attacker can obtain remote code execution on DocumentServer.

Frequently asked questions

What is CVE-2021-25833?: A file extension handling issue was found in [server] module of ONLYOFFICE DocumentServer v4.2.0.71-v5.6.0.21. The file extension is controlled by an attacker through the request data and leads to arbitrary file overwriting. Using this vulnerability, a remote attacker can obtain remote code execution on DocumentServer.
How severe is CVE-2021-25833?: CVE-2021-25833 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-2021-25833 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 44% (99th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-25833?: CVE-2021-25833 affects Onlyoffice Document Server. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-25833?: 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-2021-25833 published?: CVE-2021-25833 was published on 2021-03-01 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:onlyoffice:document_server:*:*:*:*:*:*:*:*

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