In April 2023, security researchers disclosed CVE-2023-30431, a buffer overflow vulnerability in the popular IBM Db2 database system. The issue impacts Db2 for Linux, UNIX, and Windows, including Db2 Connect Server versions 10.5, 11.1, and 11.5. Specifically, the problem lies in a command-line tool called db2set. If you administer Db2 servers, this is something you should know about.

Let’s break down what happened, how it works, and what you should do.

What is db2set?

db2set is a management utility for Db2. It is commonly used to set or view Db2 profile registry variables, which control certain behaviors of the database. This tool is usually run by database admins (DBAs) as part of setup and tuning.

The CVE in Plain English

A buffer overflow flaw exists in the db2set tool due to improper bounds checking on input data. In other words: the code does not properly check how much user-supplied data goes into a fixed memory space (a buffer). If an attacker can control the input (for example, by providing a very long registry variable), they could overwrite memory past the intended buffer. This classic software bug may allow the attacker to run their own code on the server, potentially gaining control. That could mean installing malware, stealing data, or moving deeper into a company’s internal network.

Affected versions: Db2 10.5, 11.1, 11.5 (all platforms)

- Fixed in: see IBM Security Bulletin

Technical Deep Dive: How It Happens

Software written in C or C++ often deals with raw memory. When a program receives more data than a buffer can hold and doesn’t check for it, data “overflows” into adjacent memory — sometimes overwriting code pointers or security controls.

A simplified, illustrative example in C would look like this

#include <stdio.h>
#include <string.h>

void vulnerable_db2set(char *input) {
    char buffer[256];
    // BAD: no length check
    strcpy(buffer, input);
    printf("Registry set to: %s\n", buffer);
}

int main(int argc, char **argv) {
    if (argc > 1) {
        vulnerable_db2set(argv[1]);
    } else {
        printf("Usage: %s <value>\n", argv[]);
    }
    return ;
}

Here, passing more than 256 bytes to the function would cause strcpy() to overflow the buffer, potentially overwriting function pointers or the return address on the stack.

In the real db2set, the vulnerable code could be very similar: taking input from the user (such as db2set DB2COMM=AAAAAAAAAA....), copying it unsafely into memory, and then crashing — or, if exploited properly, executing shellcode.

Who can exploit this?

- The attacker needs access to the server, either as a local user or someone who can run the db2set utility (via SSH, for instance).
- In some misconfigured environments, this could be triggered remotely if db2set is exposed (rare, but possible in legacy configs).

Craft Input: The attacker creates a long string to overflow the buffer.

2. Deliver Payload: The input is designed so part of it overwrites memory with pointers to attacker-controlled code (payload/shellcode).
3. Execute: db2set runs the payload unintentionally, giving the attacker command execution rights.

While this is a general description, here is a hypothetical command line that triggers the overflow

db2set "MYVAR=$(python3 -c 'print("A"*300)')"  # assuming buffer is 256

If you were to write an exploit, the overflow string would replace part of the memory with carefully chosen bytes so that after the program fails, your code is run.

For open-source proof-of-concept exploit ideas (for similar bugs), see

- Offensive Security Exploit Database – Buffer Overflow Examples
- Corelan Buffer Overflow Tutorials

Real-World Impact

- Privilege Escalation: If db2set is setuid root (sometimes true on older systems), a regular user could use this bug to become root.
- Data Exposure: An attacker with code execution can steal Db2 data, alter configurations, or destroy logs.

Persistence: Custom code (rootkits, backdoors) may be left behind.

IBM assigned this flaw a “high” severity; exploitability is considered significant on affected systems where user access controls are weak.

Official References

- IBM Security Bulletin: CVE-2023-30431
- National Vulnerability Database NVD - CVE-2023-30431
- IBM X-Force Exchange: 252184

How to Protect Your Systems

1. Patch Immediately: Download the fixed versions of Db2 from the IBM support site.

Conclusion

CVE-2023-30431 is a critical bug affecting IBM Db2 installations. Buffer overflows are dangerous because they enable attackers to run any code they want, often leading to full system compromise. By understanding how this vulnerability works and what exploitation looks like, you can better protect your databases and sensitive information.

Keep your Db2 servers patched and follow basic security best practices — and always be wary of inputs that can exceed the expected limits.

If you want to dive even deeper into similar exploits, check out practical buffer overflow labs at OverTheWire or Hack The Box.

Timeline

Published on: 07/10/2023 16:15:00 UTC
Last modified on: 07/31/2023 19:15:00 UTC