CVE-2021-25830

CRITICALNVD 9.89.8—
EchelonGraph scoreMEDIUM confidence

This critical-severity CVE scores 9.8 under NVD CVSS v3. EPSS exploit probability: 11.8%, top 4% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
Elevated
9.8EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 12%CVSS: 9.8Exploit: Elevated riskExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

A file extension handling issue was found in [core] module of ONLYOFFICE DocumentServer v4.2.0.236-v5.6.4.13. An attacker must request the conversion of the crafted file from DOCT into DOCX format. Using the chain of two other bugs related to improper string handling, an attacker can achieve remote code execution on DocumentServer.

CVSS v3
9.8
EG Score
9.8(medium)
EG Risk
65(Track*)
EG Risk 65/100SSVC: Track*

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity98% × 45%
Exploitation40% × 40%
Automatability30% × 15%
Action: Watch closely — could escalate to Attend.
EPSS PROB
12%
EPSS %ILE
96%
KEV
Not listed

Published

March 1, 2021

Last Modified

November 21, 2024

Advisory Details (5)

Auto-updated Aug 15, 2026
No patch confirmed yet.
generic

core/ASCOfficePPTXFile/Editor/BinaryFileReaderWriter.cpp at v5.6.4.13 · ONLYOFFICE/core · GitHub

https://github.com/ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/Editor/BinaryFileReaderWriter.cpp#L241
generic

core/ASCOfficePPTXFile/Editor/BinaryFileReaderWriter.cpp at v5.6.4.13 · ONLYOFFICE/core · GitHub

https://github.com/ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/Editor/BinaryFileReaderWriter.cpp#L1918
generic

GitHub - ONLYOFFICE/core: Server core components which are a part of ONLYOFFICE Document Server · GitHub

https://github.com/ONLYOFFICE/core
generic

GitHub - ONLYOFFICE/DocumentServer: ONLYOFFICE Docs is a free collaborative online office suite comprising viewers and editors for texts, spreadsheets and presentations, forms and PDF, fully compatible with Office Open XML formats: .docx, .xlsx, .pptx and enabling collaborative editing in real time. · GitHub

https://github.com/ONLYOFFICE/DocumentServer
generic

core/ASCOfficePPTXFile/PPTXFormat/Logic/UniFill.cpp at v5.6.4.13 · ONLYOFFICE/core · GitHub

https://github.com/ONLYOFFICE/core/blob/v5.6.4.13/ASCOfficePPTXFile/PPTXFormat/Logic/UniFill.cpp#L343

Data Freshness Timeline

(refreshed 8× in last 7d / 33× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 119 total refreshes for this CVE.

  1. 2026-08-20 22:52 UTCEPSS rescore
  2. 2026-08-19 17:01 UTCEPSS rescore
  3. 2026-08-18 13:45 UTCEPSS rescore
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  1. 2026-07-26 14:52 UTCEPSS rescore
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  5. 2026-07-23 01:58 UTCEG score recompute
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  7. 2026-07-22 14:06 UTCEPSS rescore
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  74. 2026-06-06 13:46 UTCEPSS rescore
  75. 2026-06-05 22:45 UTCEPSS rescore

Frequently asked(5)

What is CVE-2021-25830?
CVE-2021-25830 is a critical vulnerability published on March 1, 2021. A file extension handling issue was found in [core] module of ONLYOFFICE DocumentServer v4.2.0.236-v5.6.4.13. An attacker must request the conversion of the crafted file from DOCT into DOCX format. Using the chain of two other bugs related to improper string handling, an attacker can achieve remote…
When was CVE-2021-25830 disclosed?
CVE-2021-25830 was first published in the National Vulnerability Database on March 1, 2021, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-25830 actively exploited?
CVE-2021-25830 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 12% probability of exploitation in the next 30 days, which ranks it in the top 4.3% of all scored CVEs.
What is the CVSS score of CVE-2021-25830?
CVE-2021-25830 has a CVSS v3 base score of 9.8 (NVD).
How do I remediate CVE-2021-25830?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-25830, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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