Firebird Server Denial-of-Service Vulnerability (CVE-2026-28224)

CVE-2026-28224 describes a denial-of-service vulnerability affecting Firebird, an open-source relational database management system. The vulnerability exists in versions prior to 5.0.4, 4.0.7, and 3.0.14. An unauthenticated attacker can exploit this vulnerability by sending a crafted op_crypt_key_callback packet to the server. When the server receives this packet without prior authentication, the port_server_crypt_callback handler is not initialized, resulting in a null pointer dereference. This leads to a server crash, effectively causing a denial-of-service condition. The attacker only needs to know the server’s IP address and port to trigger this vulnerability. The vulnerability has been patched in Firebird versions 5.0.4, 4.0.7 and 3.0.14.

Attack Chain

1. The attacker identifies a vulnerable Firebird server by scanning for exposed ports (typically 3050).
2. The attacker establishes a TCP connection with the targeted Firebird server on the identified port.
3. The attacker crafts a malicious op_crypt_key_callback packet. This packet does not require prior authentication.
4. The attacker sends the crafted op_crypt_key_callback packet to the Firebird server.
5. Upon receiving the packet, the server attempts to process the request in the port_server_crypt_callback handler.
6. Because no prior authentication has occurred, the port_server_crypt_callback handler is not properly initialized, leading to a null pointer dereference.
7. The null pointer dereference causes the Firebird server process to crash.
8. The Firebird database server becomes unavailable, resulting in a denial-of-service condition for legitimate users.

Impact

Successful exploitation of CVE-2026-28224 results in a denial-of-service condition, rendering the Firebird database server unavailable. This can disrupt applications and services that rely on the database, leading to data access issues, application downtime, and potential data loss if proper backup and recovery mechanisms are not in place. The number of affected organizations depends on the prevalence of vulnerable Firebird versions and their exposure to the network.

Recommendation

• Upgrade Firebird servers to versions 5.0.4, 4.0.7, or 3.0.14 or later to patch CVE-2026-28224.
• Deploy the Sigma rule “Detect Unauthenticated Firebird Crypt Callback” to your SIEM to identify potential exploitation attempts targeting this vulnerability.
• Implement network segmentation and access control lists (ACLs) to restrict access to Firebird servers from untrusted networks, mitigating the risk of unauthorized exploitation (network_connection logs).
• Monitor network traffic for suspicious op_crypt_key_callback packets being sent to Firebird servers, particularly from untrusted sources (network_connection logs).