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CVE-2026-73663 – Unauthenticated SQL Injection Leading to Admin Account Takeover – FreePBX missedcal

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Summary

CVE-2026-73663 is a critical, unauthenticated SQL injection vulnerability in the missedcall module of FreePBX, the widely used open-source PBX/VoIP management platform. The flaw allows a remote, unauthenticated attacker to inject SQL via a crafted SIP From header, corrupting the FreePBX database and potentially modifying administrator control panel accounts to gain unauthorized system access. The issue carries a CVSS v4.0 base score of 9.3 (Critical).

Technical details

  • Root cause: The missedcall module logs the inbound Caller ID (CNAM) name to the database whenever a call to a monitored extension goes unanswered. The INSERT query is built by directly concatenating the caller name string into the SQL statement, with no escaping or use of bound/parameterized queries.
  • Trigger conditions: The module must be installed and actively monitoring at least one extension. An attacker simply places a call (or causes a call) to a monitored extension that goes unanswered, with a maliciously crafted Caller ID/SIP From header containing a SQL injection payload.
  • Why it’s exploitable at scale: Unlike traditional PSTN CNAM fields, which are limited to 15 characters, inbound Caller ID Name values delivered over SIP trunks or direct internet-facing SIP calling are not length-restricted, giving attackers ample room to inject arbitrary SQL payloads.
  • Attack vector: Network-based, no authentication or user interaction required (AV:N/PR:N/UI:N).
  • Impact: Successful exploitation can corrupt the FreePBX database and modify FreePBX administrator control panel accounts/credentials, allowing the attacker to obtain unauthorized administrative access to the PBX system — a potential foothold for further compromise of telephony infrastructure.
  • Root cause type: CWE-89 (Improper Neutralization of Special Elements used in an SQL Command / SQL Injection).
  • The bug has reportedly existed since the missedcall module was created in 2023.

Affected software

  • FreePBX 16 — all versions prior to 16.0.11
  • FreePBX 17 — all versions prior to 17.0.6
  • Only systems with the missedcall module installed and configured to monitor extensions are exposed.

Severity

  • CVSS v4.0 Base Score: 9.3 (Critical)
  • Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Mitigation and recommended actions

  • Immediate: Update the missedcall module / FreePBX to the patched releases — FreePBX 16.0.11 or FreePBX 17.0.6 (or later).
  • If immediate patching is not possible:
    • Restrict inbound calls so that only known, trusted SIP trunks can reach monitored extensions.
    • Enforce strong access controls on the FreePBX admin interface (User Management, VPN, MFA, or SAML) to limit the blast radius if an account is manipulated.
    • Use the FreePBX Firewall module to block untrusted/hostile network sources from reaching SIP signaling.
    • Configure Session Border Controllers (SBCs) to filter and sanitize SIP From headers before they reach the PBX.
    • If the missedcall module is not required, disable or uninstall it to eliminate exposure entirely.

References

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