CVE-2021-26084
Atlassian Confluence Server
Summary
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…
Published: 2021-08-30
Analysis
🟠 High — imminent exploitation
Weakness: Expression Language Injection (CWE-917). Injects expressions the server evaluates (Log4Shell-style).
How it's exploited: Exploitable over the network (internet-reachable), unauthenticated, no user interaction, and with low complexity.
⚠️ Critical combo: remote, unauthenticated and no interaction → trivial to automate.
Impact: Full compromise (confidentiality, integrity and availability).
Status: Exploit probability (EPSS, 30 days): 100% — high.
- Apply the vendor patch according to risk priority.
- Reduce exposure: keep it off the internet; firewall, VPN or network segmentation.
- Detect: turn this CVE into detection rules.
MITRE ATT&CK technique: T1190 · Exploit Public-Facing Application · T1059 · Command and Scripting Interpreter
Practice it in the arsenal: WAF Bypass · PowerShell Decoder · Reverse Shells
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
The vector encodes how it's exploited (translated above, in the analysis). Break it down in the CVSS tool →
Sources: CISA KEV · EPSS · FIRST.org · NVD. Analysis derived from the CVSS vector and exploitation status (no AI). Informational; always verify against the vendor's official advisory.