CVE-2021-26084: Atlassian exploited

Advisory generated from the CVE record, CISA, Exploit Observer and VEDAS: what it is, whether it is exploited, who is affected, and how to fix and detect it.

What it is

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.

Description quoted from the CVE record (assigned by atlassian, published 2021-08-30).

Weakness: CWE-917 Improper Neutralization of Special Elements used in an Expression Language Statement (‘Expression Language Injection’)

How it can be exploited

Exploitable over the network with low attack complexity needing no privileges and no user interaction. Impact: confidentiality high, integrity high, availability high. CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CISA assessment (SSVC): CISA assesses exploitation as active. Automatable: yes. Technical impact: total.

On CISA KEV since: 2021-11-03
US federal deadline: 2021-11-17
Ransomware use: Yes

Public exploit evidence (Exploit Observer)

Exploit Observer found 1 Exploit-DB entry, 1 Nuclei template, 61 code repositories and 2 research write-ups naming this CVE.

Code repositories that name a CVE are often scanners, copies or fakes, and some are malware. Read the code before running anything.

See all 70 references on Exploit Observer

Live scores

EPSS: 1.000
very likely to be attacked soon
VEDAS: 0.988
strong exploit evidence
On CISA KEV: Yes, since 2021-11-03
Detection rule: Nuclei · Suricata

EPSS (chance of attack)

VEDAS (exploit evidence)

Thin horizontal line: the “likely exploited” threshold (EPSS 0.10, VEDAS 0.5). Shaded “no data” areas are periods when cve-scores did not publish.

Who is affected

Product	Affected	Not affected
Atlassian Confluence Server	before 6.13.23 from 6.14.0 before unspecified before 7.4.11 from 7.5.0 before unspecified before 7.11.6 from 7.12.0 before unspecified before 7.12.5	Not stated
Atlassian Confluence Data Center	before 6.13.23 from 6.14.0 before unspecified before 7.4.11 from 7.5.0 before unspecified before 7.11.6 from 7.12.0 before unspecified before 7.12.5	Not stated

Version ranges exactly as the CVE record states them. “Before X” means X is the first fixed version.

How to fix it

Fixed versions stated in the CVE record: 6.13.23, unspecified, 7.4.11, 7.11.6, 7.12.5.

CISA required action: Apply updates per vendor instructions.

Vendor guidance:

https://nvd.nist.gov/vuln/detail/CVE-2021-26084

How to detect it

Nuclei template (active check)

Confluence - Expression Language Injection
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.

Name and description quoted from the template, written by VEDAS.

The template sends 1 request (POST /{{path}}); it decides using status, word matchers. Severity in the template: critical. Marked as not yet verified against a live vulnerable target.

Run it against a host you own or are authorised to test:

bash

nuclei -u https://your-host -t CVE-2021-26084.yaml

Show the template (59 lines)

yaml

id: CVE-2021-26084

info:
  name: "Confluence - Expression Language Injection"
  author: vedas-arpsyndicate
  severity: critical
  description: |
    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.
  reference:
    - https://www.exploit.observer/?keyword=CVE-2021-26084&match=exact
    - https://subdomain.center/?engine=ammonites&keyword=confluence&match=exact
  classification:
    cvss-metrics: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
    cvss-score: 9.8
    cve-id: CVE-2021-26084
    cwe-id: CWE-917
  metadata:
    verified: false
  tags: cve2021,cve,rce,confluence,injection,ognl,kev,atlassian,vkev,vuln
http:
  - raw:
      - |
        POST /{{path}} HTTP/1.1
        Host: {{Hostname}}
        Content-Type: application/x-www-form-urlencoded

        queryString=aaaa\u0027%2b#{16*8787}%2b\u0027bbb

    payloads:
      path:
        - pages/createpage-entervariables.action?SpaceKey=x
        - pages/createpage-entervariables.action
        - confluence/pages/createpage-entervariables.action?SpaceKey=x
        - confluence/pages/createpage-entervariables.action
        - wiki/pages/createpage-entervariables.action?SpaceKey=x
        - wiki/pages/createpage-entervariables.action
        - pages/doenterpagevariables.action
        - pages/createpage.action?spaceKey=myproj
        - pages/templates2/viewpagetemplate.action
        - pages/createpage-entervariables.action
        - template/custom/content-editor
        - templates/editor-preload-container
        - users/user-dark-features

    stop-at-first-match: true

    matchers-condition: and
    matchers:
      - type: word
        part: body
        words:
          - 'value="aaaa{140592=null}'

      - type: status
        status:
          - 200

CVE-2021-26084.yaml on GitHub

Suricata rules (network detection)

1 rule that alert on traffic matching this exploit: VEDAS CVE-2021-26084 Confluence - Expression Language Injection. Add them to your Suricata rule set and reload.

Show the rules

suricata

alert http $EXTERNAL_NET any -> $HTTP_SERVERS $HTTP_PORTS (msg:"VEDAS CVE-2021-26084 Confluence - Expression Language Injection"; flow:established,to_server; http.request_body; content:"queryString=aaaau0027%2b#{16*8787}%2bu0027bbb"; nocase; fast_pattern; classtype:web-application-attack; reference:cve,CVE-2021-26084; reference:url,https://www.exploit.observer/?keyword=CVE-2021-26084&match=exact; reference:url,https://subdomain.center/?engine=ammonites&keyword=confluence&match=exact; sid:1011291; rev:1;)

CVE-2021-26084.rules on GitHub

Advisories on this CVE

Synology warns of active C3RB3R (Cerber) ransomware hitting NAS devices through a patched DSM flaw (full advisory)

References

Government sources

https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26084 (government-resource)

Other references

https://jira.atlassian.com/browse/CONFSERVER-67940 (x_refsource_MISC)
http://packetstormsecurity.com/files/167449/Atlassian-Confluence-Namespace-OGNL-Injection.html (x_refsource_MISC)

Other databases

Where this comes from

This advisory is generated automatically by VEDAS from: CVE.org record, CISA KEV, cve-scores (EPSS and VEDAS), Exploit Observer, vedas-signatures. Text in quotes is reproduced from the source; everything else is a fixed template filled with source fields. Nothing here is written by a language model. Check the vendor advisory before acting, and read how VEDAS and Exploit Observer work, and their limits.