CVE-2026-28212: Firebird Database DoS Vulnerability

CVE-2026-28212 Overview

CVE-2026-28212 is a null pointer dereference vulnerability in Firebird, an open-source relational database management system. The vulnerability exists in the handling of op_slice network packets, where the server passes an unprepared structure containing a null pointer to the SDL_info() function. This results in a null pointer dereference that crashes the database server.

This vulnerability is particularly concerning because it can be exploited by unauthenticated attackers. An attacker only needs network access to the Firebird server port to send a specially crafted packet that triggers the crash, causing a denial of service condition for all database operations.

Critical Impact

Unauthenticated remote attackers can crash the Firebird database server by sending a single malicious network packet, causing complete denial of service for all connected applications and users.

Affected Products

• Firebird versions prior to 6.0.0
• Firebird versions prior to 5.0.4
• Firebird versions prior to 4.0.7
• Firebird versions prior to 3.0.14

Discovery Timeline

• April 17, 2026 - CVE-2026-28212 published to NVD
• April 20, 2026 - Last updated in NVD database

Technical Details for CVE-2026-28212

Vulnerability Analysis

The vulnerability (CWE-476: NULL Pointer Dereference) resides in Firebird's network packet processing code. When the server receives an op_slice operation packet, it processes the packet data and prepares a structure that should contain valid pointers for subsequent function calls. However, due to insufficient initialization and validation, the structure can contain a null pointer when passed to the SDL_info() function.

The SDL_info() function dereferences this pointer without proper null checks, causing the server process to crash. Since the Firebird server handles all database connections in a single process, this crash results in immediate denial of service for all connected clients and applications.

The attack requires no authentication, making it exploitable by any attacker with network access to the database port (typically port 3050 for Firebird). The low attack complexity combined with the high availability impact makes this a significant risk for exposed Firebird installations.

Root Cause

The root cause is improper initialization and validation of a data structure before it is passed to the SDL_info() function. When processing op_slice packets, the server code fails to properly prepare the structure, leaving a pointer field uninitialized (null). The SDL_info() function then attempts to dereference this null pointer without first verifying it contains a valid address, triggering the crash.

This represents a classic null pointer dereference pattern where defensive programming practices (null checks before dereferencing) were not implemented in a critical code path accessible to unauthenticated network clients.

Attack Vector

The attack is network-based and requires no authentication or user interaction. An attacker can exploit this vulnerability by:

1. Establishing a network connection to the Firebird server port (default: 3050)
2. Sending a specially crafted op_slice network packet with malformed data
3. The malformed packet causes the server to create an improperly initialized structure
4. The SDL_info() function dereferences the null pointer in the structure
5. The server crashes, denying service to all database users

The vulnerability is remotely exploitable with low complexity. The attack can be repeated to prevent the server from recovering, maintaining a persistent denial of service condition.

Detection Methods for CVE-2026-28212

Indicators of Compromise

• Unexpected Firebird server process crashes or restarts without apparent cause
• Core dump files indicating null pointer dereference in the SDL_info() function
• Network traffic containing malformed op_slice packets to the Firebird port
• Log entries showing abnormal connection attempts followed by immediate server termination

Detection Strategies

• Monitor Firebird server process stability and alert on unexpected crashes or restarts
• Implement network intrusion detection rules to identify malformed database protocol packets
• Configure process monitoring to detect repeated server crashes indicative of active exploitation
• Deploy packet inspection on the Firebird server port to identify suspicious op_slice operations

Monitoring Recommendations

• Enable detailed Firebird server logging to capture connection and operation information before crashes
• Implement network flow analysis to identify unusual traffic patterns to database ports
• Configure automated alerting for Firebird service availability degradation
• Monitor system logs for segmentation fault signals from the Firebird process

How to Mitigate CVE-2026-28212

Immediate Actions Required

• Update Firebird to the patched versions: 6.0.0, 5.0.4, 4.0.7, or 3.0.14 immediately
• Restrict network access to the Firebird server port using firewall rules to trusted IP addresses only
• Implement network segmentation to prevent unauthorized access to database servers
• Consider deploying a database proxy or load balancer that can filter malformed packets

Patch Information

Firebird has released patched versions that address this vulnerability. Organizations should upgrade to one of the following fixed versions based on their current major version:

• Firebird v3.0.14 - For 3.x installations
• Firebird v4.0.7 - For 4.x installations
• Firebird v5.0.4 - For 5.x installations
• Firebird v6.0.0 - Initial 6.x release includes the fix

For complete details, see the GitHub Security Advisory GHSA-9884-9qm3-hqch.

Workarounds

• Implement strict firewall rules to limit Firebird server access to only trusted hosts and networks
• Deploy network-level filtering to block connections from untrusted sources to port 3050
• Use a VPN or SSH tunnel for remote database access to prevent direct exposure
• Consider implementing connection rate limiting to slow potential exploitation attempts

# Example firewall configuration to restrict Firebird access
# Allow Firebird connections only from trusted application servers
iptables -A INPUT -p tcp --dport 3050 -s 10.0.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 3050 -j DROP