Firebird Database Server Slice Packet Deserialization Buffer Overflow

Firebird, a widely used open-source relational database management system, is susceptible to a critical buffer overflow vulnerability. Present in versions prior to 5.0.4, 4.0.7, and 3.0.14, the vulnerability resides within the xdr_datum() function, responsible for deserializing slice packets. This function fails to adequately validate the length of cstring data against the slice descriptor bounds. Consequently, an attacker can craft a malicious packet containing an oversized cstring, leading to a buffer overflow. An unauthenticated attacker exploiting this vulnerability can send a crafted packet to the Firebird server, potentially causing a denial-of-service condition via a crash or, more seriously, achieving arbitrary code execution on the affected system. Organizations utilizing vulnerable Firebird versions are urged to upgrade to versions 5.0.4, 4.0.7, or 3.0.14 to mitigate this risk.

Attack Chain

1. The attacker identifies a Firebird server running a vulnerable version (prior to 5.0.4, 4.0.7, or 3.0.14).
2. The attacker crafts a malicious slice packet designed to exploit the xdr_datum() function’s insufficient bounds checking. This packet includes an overly long cstring.
3. The attacker establishes a network connection to the Firebird server.
4. The attacker transmits the crafted malicious slice packet to the Firebird server.
5. The Firebird server’s xdr_datum() function processes the malicious packet without proper cstring length validation.
6. The oversized cstring overflows the allocated buffer during deserialization.
7. The buffer overflow corrupts adjacent memory regions, potentially overwriting critical data structures or executable code.
8. Depending on the overwritten memory, the server either crashes, leading to denial of service, or the attacker achieves arbitrary code execution, enabling them to gain control of the system.

Impact

Successful exploitation of this vulnerability could lead to a denial-of-service condition due to a server crash, disrupting database services and impacting applications reliant on the Firebird database. In a more severe scenario, an attacker could gain arbitrary code execution on the server, allowing them to potentially steal sensitive data, compromise the integrity of the database, or use the compromised server as a launchpad for further attacks within the network. While specific victim counts are unavailable, the widespread use of Firebird implies a significant potential impact across various sectors.

Recommendation

• Immediately upgrade Firebird servers to versions 5.0.4, 4.0.7, or 3.0.14 to patch CVE-2026-33337 and eliminate the buffer overflow vulnerability.
• Deploy the Sigma rule “Detect Firebird Slice Packet Overflow Attempt” to identify potential exploitation attempts based on anomalous network traffic patterns.
• Monitor network traffic for connections to Firebird servers originating from unexpected or untrusted sources to detect potential reconnaissance or exploitation attempts. Enable network connection logging to support this monitoring.