CVE-2021-26084
CVE-2021-26084 is a security flaw in Atlassian Confluence Server and Data Center, a wiki companies use for internal documents. Attackers can run their own code on Atlassian Confluence Server and Data Center from anywhere, without logging in. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 3 Nov 2021, and says ransomware gangs have used it.[1]
Atlassian Confluence Server and Data Center is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff. Fixed in version 6.13.23, unspecified, 7.4.11 and 7.11.6 and others.
Description
CISA calls it an object-graph navigation language (OGNL) injection in Atlassian Confluence Server and Data Center. In its words: “Atlassian Confluence Server and Data Server contain an Object-Graph Navigation Language (OGNL) injection vulnerability that may allow an unauthenticated attacker to execute code.”[1]
The CVE record adds: “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.”[2]
The underlying weakness is CWE-917, in MITRE’s list of common software weaknesses.
It scores 9.8 out of 10 on the Common Vulnerability Scoring System, which rates it critical, scored by NVD using CVSS 3.1.[2]
Affected versions
NVD’s record lists these fixed versions: in each line, everything before the version shown is affected.[2]
| Product | Fixed in |
|---|---|
| Confluence Server | 6.13.23 |
| Confluence Server | unspecified |
| Confluence Server | 7.4.11 |
| Confluence Server | 7.11.6 |
| Confluence Server | 7.12.5 |
| Confluence Data Center | 6.13.23 |
| Confluence Data Center | unspecified |
| Confluence Data Center | 7.4.11 |
Most families won’t have Atlassian Confluence Server and Data Center; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 3 Nov 2021, 65 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 17 Nov 2021 to fix it.[1] CISA says ransomware gangs have used it.
FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at over 99%. That’s in the top 1% of the flaws it scores.[4]
CISA assesses it as automatable: attackers can run it against many targets at once.
CISA doesn’t say who was attacked, or how.
Fix
Atlassian has published a fix or advice.[3] CISA’s required action: “Apply updates per vendor instructions.”[1]
- Check whether you use it.Atlassian Confluence Server and Data Center is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
- Send this page to your IT person.Ask them to confirm it’s fixed (fixed in version 6.13.23, unspecified, 7.4.11 and 7.11.6 and others), or not in use. CISA gave US government agencies until 17 Nov 2021 to fix it.
- If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.
You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 9.8.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks, noting that ransomware gangs have used it.[1] | |
| CISA’s deadline for US government agencies to fix it.[1] | |
| FIRST puts the odds of it being used in attacks in the next 30 days at over 99%.[4] |
See also
Other Atlassian Confluence Server and Data Center flaws
- CVE-2019-3398: path traversal ·
Other Atlassian flaws
- CVE-2026-21589, Atlassian products: files or directories accessible to external parties ·
- CVE-2021-26086, Atlassian Jira Server and Data Center: path traversal ·
- CVE-2023-22527, Atlassian Confluence Data Center and Server: template injection ·
- CVE-2023-22518, Atlassian Confluence Data Center and Server: improper authorization ·
- CVE-2023-22515, Atlassian Confluence Data Center and Server: broken access control ·
Similar flaws
- CVE-2021-45046, Apache Log4j2: deserialization of untrusted data ·
- CVE-2020-17530, Apache Struts: remote code execution ·
- CVE-2020-10199, Sonatype Nexus Repository: remote code execution ·
Added the same day
- CVE-2021-42258, BQE BillQuick Web Suite: SQL injection ·
- CVE-2021-42013, Apache HTTP Server: path traversal ·
- CVE-2021-41773, Apache HTTP Server: path traversal ·
- CVE-2021-40539, Zoho ManageEngine: aDSelfService plus authentication bypass ·
- CVE-2021-40444, Microsoft MSHTML: remote code execution ·
Every Atlassian flaw on CISA’s list · Everything added in November 2021
References
- ^ Cybersecurity and Infrastructure Security Agency. “Atlassian Confluence Server and Data Center Object-Graph Navigation Language (OGNL) Injection Vulnerability”. Known Exploited Vulnerabilities Catalog, added 3 Nov 2021.
- ^ National Institute of Standards and Technology. “CVE-2021-26084 Detail”. National Vulnerability Database, published 30 Aug 2021.
- ^ Atlassian. Advisories and fixes: jira.atlassian.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 1.000, percentile 100.0, 31 Oct 2026.
- CVE Program. “CVE-2021-26084”. The official CVE record.
This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.