CVE-2021-26084
Atlassian Confluence Server and Data Center Object-Graph Navigation Language (OGNL) Injection Vulnerability
Description
CVE-2021-26084 is a CRITICAL vulnerability affecting Atlassian Confluence Server and Data Center, carrying a CVSS 3.1 score of 9.8. Atlassian Confluence Server and Data Server contain an Object-Graph Navigation Language (OGNL) injection vulnerability that may allow an unauthenticated attacker to execute code. Affected products include atlassian confluence data center (< 6.13.23; >= 6.14.0, < 7.4.11; >= 7.5.0, < 7.11.6; >= 7.12.0, < 7.12.5), atlassian confluence server (< 6.13.23; >= 6.14.0, < 7.4.11; >= 7.5.0, < 7.11.6; >= 7.12.0, < 7.12.5). This CVE is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog with a remediation deadline of 2021-11-17. With an EPSS score of 0.94420 (99.98th percentile), this vulnerability demonstrates significant real-world exploitation activity and should be prioritized for immediate remediation.
KEV Information
CVSS Score
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:HOpen in CalculatorCWEs
Affected Products
| Vendor | Product | Version |
|---|---|---|
| atlassian | confluence data center | < 6.13.23; >= 6.14.0, < 7.4.11; >= 7.5.0, < 7.11.6; >= 7.12.0, < 7.12.5 |
| atlassian | confluence server | < 6.13.23; >= 6.14.0, < 7.4.11; >= 7.5.0, < 7.11.6; >= 7.12.0, < 7.12.5 |
Multiple CVSS Assessments
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
References
- http://packetstormsecurity.com/files/167449/Atlassian-Confluence-Namespace-OGNL-Injection.html(Exploit, Third Party Advisory, VDB Entry)
- https://jira.atlassian.com/browse/CONFSERVER-67940(Issue Tracking, Patch, Vendor Advisory)
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26084(US Government Resource)
Weakness Type
CWE-917: Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection')
CVE-2021-26084 is classified under CWE-917 — Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection'). This weakness category describes flaws where software constructs all or part of an expression language statement from user-controllable input without neutralizing special elements. Expression Language injection can allow an attacker to execute arbitrary code or access unauthorized data through the evaluation engine.
In the context of Atlassian Confluence Server and Data Center, this weakness is particularly concerning because OGNL injection in Confluence Server allows unauthenticated attackers to execute arbitrary code. OGNL (Object-Graph Navigation Language) is deeply integrated into the application framework, and injection flaws can bypass security controls entirely. The combination of unauthenticated access and code execution makes this vulnerability extremely dangerous for internet-facing Confluence instances.
Impact Analysis
CVE-2021-26084 carries a CVSS 3.1 score of 9.8 (CRITICAL) with Unchanged Scope.
Confidentiality (HIGH): Successful exploitation grants the attacker extensive access to sensitive data processed by the affected system, including configuration files, credentials, and potentially data from connected systems.
Integrity (HIGH): Attackers can modify critical system files, install backdoors, alter configurations, or deploy malware on affected systems.
Availability (HIGH): Complete disruption of the affected service or system is possible, including denial of service, system crashes, or rendering the product inoperable.
Scope Unchanged: The vulnerability's scope is Unchanged (U), meaning exploitation is contained within the vulnerable component. The impact, while significant, is limited to the affected product environment itself.
With an EPSS score of 0.94420 (99.98th percentile), this vulnerability ranks among the most likely to be exploited in real-world attacks, underscoring the urgency of remediation.
Exploit Maturity
CVE-2021-26084 has confirmed active exploitation in the wild and is listed in CISA's Known Exploited Vulnerabilities catalog.
Exploit status: This vulnerability has been actively exploited, as confirmed by its inclusion in the KEV catalog. The EPSS score of 0.94420 (99.98th percentile) places it among the most exploited vulnerabilities tracked.
Ransomware association: CVE-2021-26084 has been associated with ransomware campaigns. This significantly increases the risk profile, as ransomware operators actively target this vulnerability for initial access or lateral movement within compromised environments.
Attack surface: The vulnerability requires network access with low attack complexity and no authentication, requiring no user interaction. Organizations should assume exploitation tools exist and are being actively used by threat actors.
KEV deadline: CISA required federal agencies to remediate this vulnerability by 2021-11-17. All organizations should treat this deadline as a strong recommendation for their own remediation timelines.
Remediation
- Apply vendor patches immediately. Apply updates per vendor instructions. Consult the vendor advisory for specific patch guidance and updated versions.
- Verify affected product versions in your environment. Identify all instances of Atlassian Confluence Server and Data Center in your infrastructure (affected versions: atlassian confluence data center (< 6.13.23; >= 6.14.0, < 7.4.11; >= 7.5.0, < 7.11.6; >= 7.12.0, < 7.12.5), atlassian confluence server (< 6.13.23; >= 6.14.0, < 7.4.11; >= 7.5.0, < 7.11.6; >= 7.12.0, < 7.12.5)). Use asset inventory and vulnerability scanning tools to ensure no instances are missed.
- Implement interim mitigations if patching is delayed. If immediate patching is not feasible, apply network-level controls such as restricting access to the affected component, enabling enhanced logging, and monitoring for indicators of compromise.
- Scan for signs of prior exploitation. Given the confirmed active exploitation of this vulnerability, review system logs and security monitoring data for evidence of compromise. Conduct a thorough investigation if any suspicious activity is detected.
- Update detection signatures and monitoring rules. Ensure intrusion detection and prevention systems, endpoint detection tools, and SIEM rules are updated to detect exploitation attempts targeting CVE-2021-26084.
- Conduct a post-remediation review. After patching, verify the fix is effective and document the remediation actions taken. Update your vulnerability management records and assess whether any additional hardening measures are warranted.
Technical Details
CVE-2021-26084 is a CRITICAL-severity vulnerability in Atlassian Confluence Server and Data Center that can be exploited remotely over the network without physical access. The attack complexity is low, meaning no specialized conditions or preparation are required beyond the attack prerequisites. No prior authentication or privileges are needed to initiate the attack. No user interaction is required, allowing for fully automated exploitation.
Technical mechanism: 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.
CVSS 3.1 vector analysis: The vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H reflects an Attack Vector of NETWORK, Attack Complexity of LOW, Privileges Required of NONE, User Interaction of NONE, Scope UNCHANGED, and impact ratings of HIGH/HIGH/HIGH for Confidentiality/Integrity/Availability respectively.
Frequently Asked Questions
Is CVE-2021-26084 being actively exploited?
Yes, CVE-2021-26084 is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, confirming active exploitation in the wild. The EPSS score of 0.94420 (99.98th percentile) further indicates significant exploitation probability. This vulnerability has also been linked to ransomware campaigns. Organizations should treat this as an urgent priority requiring immediate remediation.
What products are affected by CVE-2021-26084?
The affected products include atlassian confluence data center (< 6.13.23; >= 6.14.0, < 7.4.11; >= 7.5.0, < 7.11.6; >= 7.12.0, < 7.12.5), atlassian confluence server (< 6.13.23; >= 6.14.0, < 7.4.11; >= 7.5.0, < 7.11.6; >= 7.12.0, < 7.12.5). Organizations running any of these versions should verify their exposure and prioritize remediation. Check vendor advisories for the complete and most current list of affected versions.
How do I fix CVE-2021-26084?
Apply updates per vendor instructions. Ensure all affected instances of Atlassian Confluence Server and Data Center are identified using vulnerability scanning and asset management tools. If immediate patching is not possible, implement network-level mitigations and enhanced monitoring. After patching, verify the fix and scan for indicators of prior compromise.
How severe is CVE-2021-26084?
CVE-2021-26084 is rated CRITICAL with a CVSS 3.1 score of 9.8. Its EPSS score of 0.94420 places it in the 99.98th percentile for exploitation likelihood. The vulnerability has confirmed active exploitation in the wild and was required to be remediated by federal agencies by 2021-11-17 per CISA's KEV directive.
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