CriticalCVE-2021-26084

    Atlassian Confluence Server: Code Execution (CVE-2021-26084)

    Published In CISA KEV since Sources: SingCERT, CVE.org

    What is affected, what to do

    An OGNL injection vulnerability in Atlassian Confluence Server and Data Center allows an unauthenticated attacker to execute arbitrary code. This affects versions before 6.13.23, from 6.14.0 to 7.4.11, from 7.5.0 to 7.11.6, and from 7.12.0 to 7.12.5. The vulnerability is actively exploited in ransomware campaigns. It is critical to update affected systems to version 6.13.23 or higher to mitigate this risk.

    The vulnerability is being actively exploited; treat it as a priority. CISA lists it as used in ransomware campaigns. Update Atlassian Confluence Server to version 6.13.23, Atlassian Confluence Server to version 7.4.11, Atlassian Confluence Server to version 7.11.6. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Atlassian Confluence Server lt *..6.13.23
    • Atlassian Confluence Server eq 6.14.0..6.14.0
    • Atlassian Confluence Server lt *..7.4.11
    • Atlassian Confluence Server eq 7.5.0..7.5.0
    • Atlassian Confluence Server lt *..7.11.6
    • Atlassian Confluence Server eq 7.12.0..7.12.0
    • Atlassian Confluence Server lt *..7.12.5
    • Atlassian Confluence Data Center lt *..6.13.23
    • Atlassian Confluence Data Center eq 6.14.0..6.14.0
    • Atlassian Confluence Data Center lt *..7.4.11
    • Atlassian Confluence Data Center eq 7.5.0..7.5.0
    • Atlassian Confluence Data Center lt *..7.11.6
    • Atlassian Confluence Data Center eq 7.12.0..7.12.0
    • Atlassian Confluence Data Center lt *..7.12.5
    Fixed in
    • Atlassian Confluence Server 6.13.23
    • Atlassian Confluence Server 7.4.11
    • Atlassian Confluence Server 7.11.6
    • Atlassian Confluence Server 7.12.5
    • Atlassian Confluence Data Center 6.13.23
    • Atlassian Confluence Data Center 7.4.11
    • Atlassian Confluence Data Center 7.11.6
    • Atlassian Confluence Data Center 7.12.5

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    9.8

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: NVD, CVSS v3

    9.8

    CVSS v3

    Severity Critical on the scale from 0 to 10.

    Source: SingCERT, CVE.org

    —

    EPSS score

    No value is available for this vulnerability.

    Show all metrics
    Severity
    Critical
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    253.98 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    actively exploitedSource: ANSSI / CERT-FR How we classify
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    9.8 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    9.8
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    99.99
    Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    Actively exploited
    Published
    In CISA KEV since

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This CVE sits on KEV because it is unauthenticated and network-reachable (CVSS vector AV:N/PR:N/UI:N), a public exploit has been weaponised in commodity mining and ransomware campaigns since September 2021, and CISA explicitly flags ransomware use. EPSS places it among the very highest exploitation-likelihood CVEs — any exposed vulnerable instance should be assumed to be attacked within hours of becoming reachable. Target profile is any internet-facing Confluence deployment; in NIS2-scope organisations these are typically collaboration backbones with Kerberos or LDAP SSO, making the host a prime pivot into Active Directory. Treat as P1/Critical with a 24-hour SLA to either patched or network-removed state, independent of any compensating controls.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Upgrade Confluence Server and Data Center to a vendor-fixed release: 6.13.23, 7.4.11, 7.11.6, 7.12.5 or any 7.13.0+ build. Record the exact build number in the change ticket.
      • If a patch window is not immediately available, remove internet exposure at the perimeter (reverse proxy, WAF, firewall) and restrict Confluence to internal networks or VPN access. Pay particular attention to TCP 8090 (default Tomcat) and the fronting 443/80.
      • Run Atlassian's temporary mitigation script (cve-2021-26084-update.sh on Linux, .ps1 on Windows) if patching is delayed — it replaces the vulnerable Tomcat templates and restarts Confluence cleanly.
      • Treat the Confluence host as potentially compromised: inspect the process tree under the service account (typically confluence) for sh, bash, cmd.exe, powershell.exe, curl, wget or python spawned by java. On any hit, isolate the host and capture a forensic image.
      • Rotate service credentials (Confluence DB user, LDAP bind, SMTP, API tokens, Marketplace app keys) and invalidate all persistent user sessions.
      • Verify that recent backups exist on immutable or air-gapped storage — CISA has flagged this CVE as used in ransomware operations.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: place Confluence in a dedicated VLAN with explicit egress allowlisting (Atlassian Marketplace, internal mail, DB only). This neutralises the C2 callbacks and crypto-miner payloads that have been widely observed with this CVE.
      • WAF / reverse proxy rule: block HTTP requests carrying OGNL-style markers — ${ or URL-encoded %24%7B in URI, query or body, especially on /pages/createpage-entervariables.action, /pages/doenterpagevariables.action, /pages/createpage.action. ModSecurity example: SecRule REQUEST_URI|ARGS "@rx \\\$\{.*\}" "id:1026084,deny,log".
      • Path whitelisting at the reverse proxy: pass only documented Confluence URIs, inspect every .action request for OGNL metacharacters (#, @, $, {, }).
      • Run Tomcat/Confluence as a dedicated low-privilege user (not root) with an enforcing AppArmor or SELinux profile; restrict write access to /opt/atlassian/confluence/confluence/WEB-INF/ to deployment windows only.
      • Endpoint hardening: EDR policy that blocks java as parent of shell interpreters or download tools. Force outbound DNS through a central resolver with threat-feed blocking.
      • Minimise installed Marketplace apps — each additional app enlarges the OGNL attack surface through extra Velocity templates.

    3. Runbook step 3

      Detection rules

      • Web access logs (Apache/Nginx/Tomcat): look for \$\{.*\} or URL-encoded %24%7B in URI or query on .action endpoints. KQL: W3CIISLog | where csUriQuery contains "%24%7B" or (csUriStem contains ".action" and csUriQuery matches regex @"\$\{.*\}").
      • Sysmon EID 1 or Linux auditd execve: java spawning /bin/sh, /bin/bash, cmd.exe, powershell.exe, curl, wget, nc, python. Sigma shape: parent_image endswith '\\java.exe' and image endswith ('\\cmd.exe','\\powershell.exe').
      • Netflow/Zeek: egress from the Confluence host to non-business IPs, especially crypto-mining pools (ports 3333, 4444, 5555, 7777, 14444) and Tor entry nodes.
      • File-integrity monitoring on /opt/atlassian/confluence/confluence/WEB-INF/, /temp/ and /tmp/ for newly created .jsp, .sh, .elf or .class files outside deployment windows (auditd -w ... -p wa).
      • Confluence application log atlassian-confluence.log: Velocity/OGNL exceptions with stack traces from com.opensymphony.webwork or ognl.OgnlException following HTTP requests containing ${ indicate exploitation attempts.

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    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.

    Source: CSA/SingCERT, NVD (NIST), cvelistv5, CISA KEV Catalog, CVE.org (MITRE)

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    AtlassianConfluence Data Center
    • < 6.13.23
    • < 7.4.11
    • 6.14.0
    • < 7.12.5
    • 7.5.0
    • < 7.11.6
    • 7.12.0
    • 6.13.23
    • 7.4.11
    • —
    • 7.12.5
    • —
    • 7.11.6
    • —
    AtlassianConfluence Server
    • < 7.11.6
    • 7.5.0
    • 6.14.0
    • < 6.13.23
    • < 7.12.5
    • 7.12.0
    • < 7.4.11
    • 7.11.6
    • —
    • —
    • 6.13.23
    • 7.12.5
    • —
    • 7.4.11
    atlassianconfluence_data_center
    • 7.5.0 – < 7.11.6
    • 7.12.0 – < 7.12.5
    • < 6.13.23
    • 6.14.0 – < 7.4.11
    • 7.11.6
    • 7.12.5
    • 6.13.23
    • 7.4.11
    atlassianconfluence_server
    • 7.12.0 – < 7.12.5
    • 6.14.0 – < 7.4.11
    • < 6.13.23
    • 7.5.0 – < 7.11.6
    • 7.12.5
    • 7.4.11
    • 6.13.23
    • 7.11.6

    Vendors and products

    Public exploit references

    Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

    Public exploit references
    CISA KEV CatalogCISA Known Exploited Vulnerability (opens in a new tab)cisa.govactively exploited
    ANSSI / CERT-FRLicence Ouverte 2.0, as of CERTFR-2021-ALE-018 – Vulnérabilité dans Atlassian Confluence Server et Data Center (clôturée 2022-01-05) (opens in a new tab)cert.cyber.gouv.fractively exploited
    Packet StormAtlassian Confluence Namespace OGNL Injection (opens in a new tab)packetstormsecurity.comPoC (publicly reported)reported, not verified—

    References & sources

    • jira.atlassian.combrowse/CONFSERVER-67940x_refsource_MISC, Issue tracking, Patch, Vendor advisory
    • packetstormsecurity.comfiles/167449/Atlassian-Confluence-Namespace-OGNL-Injection.htmlx_refsource_MISC, Exploit, Third-party advisory, Vulnerability database
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26084government-resource, US government resource
    • cert.cyber.gouv.frANSSI / CERT-FR: CERTFR-2021-ALE-018 – Vulnérabilité dans Atlassian Confluence Server et Data Center (clôturée 2022-01-05)cert-fr
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