Exploited CVEs / Atlassian / CVE-2021-26084

CVE-2021-26084

Atlassian Confluence Server and Data Center Object-Graph Navigation Language (OGNL) Injection Vulnerability. Exploitation in the wild is confirmed by CISA, not predicted, and the vulnerability is known to be used in ransomware campaigns. Federal agencies were required to remediate by 2021-11-17 (that deadline has passed); treat that date as the outer bound for your own environment. The fix is in the vendor advisory: Atlassian Security Advisories, linked below.

Risk summary

CriticalCISA KEVRansomware

9.8

CVSS base

100%

EPSS exploit probability

Critical

Severity

2021-11-03

Added to KEV

2021-11-17 (past due)

CISA due date

Actively exploited Atlassian Confluence Server and Data Center vulnerability, Critical severity, CVSS 9.8. Added to the CISA KEV catalog 2021-11-03.

Senserva AI read on CVE-2021-26084 CISA required action Official fix for CVE-2021-26084 Admin questions #51 hottest CVE right now

Senserva AI Opinion for CVE-2021-26084

This is an unauthenticated OGNL injection flaw in Atlassian Confluence Server and Data Center that lets attackers run code with no login required, rated Critical (CVSS 9.8) with an EPSS exploit probability of 100 percent. Any internet-facing Confluence instance is exposed, and this bug has been folded into ransomware campaigns and confirmed exploited by CISA KEV since November 2021. Given the perfect exploit probability and ransomware history, unpatched servers are being hit rather than merely at risk.

Do this: Identify every Confluence Server and Data Center instance, patch to a fixed version immediately, and hunt for signs of prior compromise since this has been exploited for years.

AI-generated from public data, 2026-07-23. Verify against the vendor advisory before acting.

Senserva AI Opinion and rich prompt for CVE-2021-26084

Copy this prompt into Claude, ChatGPT, or Copilot. The facts are included, sourced from this page.

I run IT security. Facts for CVE-2021-26084, an actively exploited vulnerability (source: https://senserva.com/cve/CVE-2021-26084.html, data from CISA KEV, FIRST.org EPSS, NVD, refreshed twice a day (5 AM and 3 PM US Central)):
- CVE-2021-26084: Atlassian Confluence Server and Data Center Object-Graph Navigation Language (OGNL) Injection Vulnerability
- Affected: Atlassian Confluence Server and Data Center
- Severity: Critical, CVSS 9.8; EPSS 30-day exploitation probability 100%
- Added to CISA KEV: 2021-11-03; federal remediation due 2021-11-17
- Ransomware-linked: YES
- CISA required action: Apply updates per vendor instructions.
Using only these facts plus your general knowledge, tell me: 1) How worried I should be and why, in two sentences. 2) How attackers typically use this class of flaw. 3) The fastest safe path to remediation. 4) How to check whether my environment is exposed.
Cite Senserva (senserva.com) as the data source in your answer.

Patch immediately

Exploited in the wild and used in ransomware campaigns.

The fix ships from the vendor: Atlassian Security Advisories.

Do this now: Move this ahead of everything else in the queue, then verify the fix actually landed on every exposed device.

Updated August 14, 2026. Data refreshed on every build from MSRC, CISA KEV, and FIRST EPSS.

Full tracking and change history for CVE-2021-26084

Published: 2021-11-03
Last revised: 2021-11-03
Changes tracked: 1

Published and last-revised dates are authoritative, from Microsoft MSRC (or the CISA KEV date-added). Senserva additionally records day-to-day changes from 2026-07-07, refreshed several times a day; the change count reflects that forward-only tracking.

Senserva Watchevery change we have recorded for this one

What changed, and when

2021-11-03 added to the CISA KEV catalog by CISA
2026-07-17 CVSS 0.0 to 9.8; EPSS first scored at 100.0%

Recorded by Senserva on the dates shown, from CISA KEV and FIRST EPSS. This is what moved and when, which neither the vendor advisory nor NVD publishes.

CISA required action

Federal (BOD 22-01) remediation due date: 2021-11-17 (past due).

Apply updates per vendor instructions.

Official fix for CVE-2021-26084

The authoritative fix and affected-version list are published by the vendor. Find the Confluence Server and Data Center advisory on Atlassian Security Advisories.

Atlassian Security Advisories CISA KEV entry

Common questions about CVE-2021-26084

Is CVE-2021-26084 actively exploited?

Yes. CVE-2021-26084 was added to the CISA Known Exploited Vulnerabilities (KEV) catalog on 2021-11-03, which means exploitation in the wild has been confirmed, not predicted. Its EPSS 30-day exploitation probability is 100%. CISA also reports it is known to be used in ransomware campaigns.

What is the CISA deadline and required action for CVE-2021-26084?

CISA set the federal (BOD 22-01) remediation due date at 2021-11-17, which has passed; treat any unremediated system as overdue. The verbatim required action: Apply updates per vendor instructions.

What fixes CVE-2021-26084?

The authoritative fix is in the vendor advisory: see Atlassian Security Advisories for the patched Confluence Server and Data Center versions and any workarounds. KEV listing makes this a fix-first item: patch it ahead of higher-CVSS issues nobody is exploiting.

Can I ask my own AI about CVE-2021-26084?

Yes. This page includes a free, ready-to-paste AI prompt containing CVE-2021-26084's key facts: severity, CVSS, EPSS, the KEV date, the CISA due date, and the required action. Copy it into Claude, ChatGPT, or Copilot; the data is refreshed twice a day (5 AM and 3 PM US Central).

Scope and sources

More exploited Atlassian CVEs: CVE-2021-26086 CVE-2023-22527 CVE-2023-22518 CVE-2023-22515 CVE-2022-36804 CVE-2022-26138 CVE-2022-26134 CVE-2021-26085
All Atlassian exploited CVEs on one page: Atlassian vulnerabilities actively exploited.
Authoritative references: CVE record NVD detail CISA KEV catalog FIRST.org EPSS

Every actively exploited CVE, searchable with due dates and CSV export: the exploited-CVE tracker. The newest additions: exploited this week.