Threats / Atlassian / CVE-2021-26084
CVE-2021-26084
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-06-22
Atlassian Confluence Server and Data Center vulnerability
Atlassian Confluence Server and Data Center are vulnerable to unauthenticated OGNL injection, allowing remote code execution. This vulnerability has been actively exploited in ransomware campaigns.
Verdict
Today item, not a backlog item.
An unauthenticated attacker can inject malicious Object-Graph Navigation Language expressions into Confluence, achieving arbitrary code execution on the server. The high EPSS score and confirmed wild exploitation indicate immediate risk to unpatched instances.
CISA KEV Yes · 2021-11-033Ransomware use Flagged3EPSS 0.99999 (verify live)4Exploit Weaponized · public PoC5
01
Is it exploitable?
— the evidence, ranked above the scoreExploit available
Fully weaponized — public exploit code is cataloged for this vulnerability.We link the existence of the exploit; we do not host or redistribute payloads.
Reported exploitation
951 independent public reports of in-the-wild exploitation are cataloged.Distinct reporting sources (vendor, incident response, government); open them for the underlying claims.
Exploited in the wild
Listed in the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03), flagged for known ransomware use.
Probability (EPSS)
EPSS 0.99999 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
Severity / affected
Affected: Atlassian, Confluence Server and Data Center. Confirm exact fixed builds in the vendor advisory.
Weakness (CWE)
Mapped to CWE-917 Expression Language Injection — weakness family: Injection.CWE assignment from the public NVD record; the weakness class drives how the flaw is exploited.
02
Who’s exploiting it?
— attribution turns risk into urgencyAPT40 State-sponsored (PRC)
The CISA-led joint advisory AA24-190A names APT40 (tracked in ATT&CK as Leviathan) as a PRC Ministry of State Security group that rapidly weaponizes newly public vulnerabilities, naming the ProxyShell Exchange chain, Log4Shell, and Atlassian Confluence CVEs alongside the group.14
03
Why it matters
— the attack path, told twice: adversary, then board1
Front door — unauthenticated access narrative 1
Attacker
I craft a malicious OGNL expression and send it to an unauthenticated endpoint in Confluence.
Business
The organization's Confluence instance is compromised without requiring valid credentials, expanding the attack surface to any internet-facing deployment.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
My injected expression executes arbitrary code with the privileges of the Confluence process.
Business
Attackers gain full control of the server, enabling data theft, lateral movement, and installation of persistent backdoors.
3
Lateral reach — past segmentation narrative 3
Attacker
I deploy ransomware or encrypt critical collaboration data stored in Confluence.
Business
Business operations halt as teams lose access to documentation, project plans, and institutional knowledge; recovery requires costly incident response and potential ransom negotiation.
04
What to do
— defensible action- Remediate per the vendor advisory — confirm the fixed build for your version and verify exposure.1
Say it to the boardA vulnerability with this evidence profile is a defensible budget line, not a backlog ticket — fund the change against the proof above.
05