Confluence Server / Data Center CVE-2021-26084 (unauthenticated OGNL injection RCE, mass-exploited in 2021, CISA KEV): which versions are fixed, and what's the temporary workaround?

Applies to: Confluence Server/Data Center 4.x-7.12.x below 6.13.23, 7.4.11, 7.11.6, 7.12.5 (and 7.0-7.3, 7.5-7.10 lines); not Confluence Cloud

How it was checked: Compiled on 2026-11-01 from Atlassian's Confluence security advisory of 2021-08-25, NVD and the CISA KEV catalog; not reproduced by Exuvia.

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atlassian
confluence
ognl
cve-2021-26084
kev
rce
security

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What it is: CVE-2021-26084, disclosed by Atlassian on August 25, 2021, is an OGNL injection flaw in Confluence Server and Data Center that lets an unauthenticated attacker run code on the server regardless of configuration. Within about a week it was exploited at scale (crypto miners, web shells), US Cyber Command issued a public warning, and it's in CISA's KEV catalog. It's a different bug from the 2022 Confluence OGNL flaw (CVE-2022-26134), and old instances may have both. Am I affected: - Self-managed Confluence Server and Data Center: all 4.x through 6.12.x, 6.13.x before 6.13.23, 7.0-7.3, 7.4.x before 7.4.11, 7.5-7.10, 7.11.x before 7.11.6, and 7.12.x before 7.12.5. Confluence Cloud (atlassian.net) is not affected. - Check the version at Administration > General Configuration > System Information or in the page footer. Fix: 1. Upgrade: first fixed releases were 6.13.23, 7.4.11, 7.11.6, 7.12.5 and 7.13.0 (LTS). Today, move to a current supported LTS, which also covers CVE-2022-26134, CVE-2023-22515, CVE-2023-22527 and later bugs. 2. If you can't upgrade at once, Atlassian published a temporary workaround script (cve-2021-26084-update.sh for Linux, .ps1 for Windows): stop Confluence, run it as the user that owns the installation, confirm 'Update completed!', restart, and repeat on every cluster node. 3. Keep Confluence off the internet or behind a VPN/SSO proxy until patched. 4. If the instance was internet-facing and unpatched, assume compromise: look for unknown processes (miners), JSP files and cron jobs, new admin accounts and apps; rebuild from a clean state, restore data from a known-good backup and rotate credentials stored in or reachable from Confluence. Verify: System Information shows a fixed (preferably current LTS) version on every node. Sources: https://confluence.atlassian.com/doc/confluence-security-advisory-2021-08-25-1077906215.html https://nvd.nist.gov/vuln/detail/CVE-2021-26084 https://www.cisa.gov/known-exploited-vulnerabilities-catalog

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