CVE-2021-26084 — Confluence Data Center
CRITICALCVE-2021-26084 is a critical-severity (CVSS 9.8) Expression Language Injection vulnerability in atlassian confluence data center. It is in CISA's Known Exploited Vulnerabilities catalog (added 2021-11-03) and has been used in ransomware campaigns — treat it as actively exploited and patch now. A fix is available — see the affected versions and patch details below.
In affected versions of Confluence Server and Data Center, an OGNL injection vulnerability exists that would allow an unauthenticated attacker to execute arbitrary code on a Confluence…
Exploitation Status
Actively exploited in the wild
- Confirmed by CISA's Known Exploited Vulnerabilities catalog on 2021-11-03 — including use in ransomware campaigns. Federal agencies were required to remediate by 2021-11-17.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA (KEV catalog and SSVC triage) for CVE-2021-26084.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-26084 by exploitation likelihood (EPSS) against impact (CVSS). In the shaded patch-first corner (EPSS 50%+, CVSS 7.0+).
Where this sits among everything scored
Of 394,415 CVEs with a current EPSS score, this one falls in the ≥ 90% band (highlighted). Counts from FIRST.org, log-scaled.
Description
In affected versions of Confluence Server and Data Center, an OGNL injection vulnerability exists that would allow an unauthenticated attacker to execute arbitrary code on a Confluence Server or Data Center instance. The affected versions are before version 6.13.23, from version 6.14.0 before 7.4.11, from version 7.5.0 before 7.11.6, and from version 7.12.0 before 7.12.5.
Affected Products
confluence data centeratlassianconfluence serveratlassianResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Confluence Server 7.12.4 - 'OGNL injection' Remote Code Execution (RCE) (Unauthenticated)
by Fellipe Oliveira · Sep 1, 2021
Detection & mitigation playbook
Vendor / applianceDetect
Inventory every atlassian confluence data center deployment and check each version against the affected-products list above.
Fix
Apply the atlassian confluence data center security patch or hotfix for CVE-2021-26084 on the affected version, following the vendor advisory for your exact build.
Workarounds
Stop passing untrusted input into the interpreter or shell: call the affected binary with an argument array rather than a composed command string, reject anything outside a strict allowlist of expected values, and run the component under an account that cannot reach beyond the work it legitimately does. Alongside that, restrict the management interface to trusted networks and apply the vendor's recommended configuration mitigations.
How to detect CVE-2021-26084
A community-maintained Nuclei template exists for this CVE. You can scan for it directly:
nuclei -id cve-2021-26084 -u https://target- Template
- Confluence Server - Remote Code Execution
- Severity
- critical
- Impact
- Successful exploitation of this vulnerability could allow an attacker to execute arbitrary code on the affected server.
- Remediation
- Apply the latest security patches provided by Atlassian to mitigate this vulnerability.
Template by ProjectDiscovery nuclei-templates (dhiyaneshDk, philippedelteil), MIT licensed. View the full template. Scan only systems you are authorised to test.
Frequently Asked Questions
Is CVE-2021-26084 being exploited in your environment?
Detect and block the exploit chain at execution, on systems you cannot patch yet.