What is CVE-2021-26084?

CVE-2021-26084 is a critical-severity vulnerability in Atlassian Confluence Data Center, classified under Improper Neutralization of Special Elements used in an Expression Language Statement (Expression Language Injection). CVSS score: 9.8/10. Published 2021-08-30.

How severe is CVE-2021-26084?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Is CVE-2021-26084 known to be exploited?

Yes. CVE-2021-26084 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03), indicating it is being actively exploited. 215 public proof-of-concept repositories are indexed.

RCE in Atlassian Confluence Data Center

CVE-2021-26084

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…

Vulnerability class: Log4Shell (CVE-2021-44228)

EPSS: 1.000 (100.0th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

Affected products

Atlassian Confluence Data Center — versions unspecified, 6.14.0, 7.5.0
Atlassian Confluence_data_center
Atlassian Confluence Server — versions unspecified, 6.14.0, 7.5.0
Atlassian Confluence_server

Weakness classification (CWE)

CWE-917 — Improper Neutralization of Special Elements used in an Expression Language Statement (Expression Language Injection)

CISA KEV (Known Exploited Vulnerabilities)

This CVE is on the CISA KEV catalog, added on 2021-11-03. CISA KEV inclusion means CISA has confirmed in-the-wild exploitation; US federal agencies are required to remediate within a published due date.

BOD 22-01 due date: 2021-11-17.

Required action: Apply updates per vendor instructions.

Known ransomware campaign use: yes.

Public proof-of-concept exploits

References

security@atlassian.com (Patch, x_refsource_MISC, Issue Tracking, Vendor Advisory)
security@atlassian.com (Exploit, VDB Entry, Third Party Advisory, x_refsource_MISC)
134c704f-9b21-4f2e-91b3-4a467353bcc0 (US Government Resource)

Frequently asked questions

What is CVE-2021-26084?: CVE-2021-26084 is a critical-severity vulnerability in Atlassian Confluence Data Center, classified under Improper Neutralization of Special Elements used in an Expression Language Statement (Expression Language Injection). CVSS score: 9.8/10. Published 2021-08-30.
How severe is CVE-2021-26084?: Critical severity. CVSS v3 base score is 9.8 out of 10.
Is CVE-2021-26084 known to be exploited?: Yes. CVE-2021-26084 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03), indicating it is being actively exploited. 215 public proof-of-concept repositories are indexed.