MariaDB is one of the world’s most popular open-source relational database management systems, used by enterprises everywhere for its reliability and speed. But like any software, MariaDB can harbor critical bugs. In early 2022, security researchers found CVE-2022-27457, a serious Use-After-Free (UAF) vulnerability affecting MariaDB Server version v10.6.3 and below. This article explores in plain language what this bug is, why it matters, and how it can be exploited — including exclusive code snippets for those looking to understand or reproduce the issue (for educational purposes only).

What Is CVE-2022-27457?

A use-after-free bug happens when a program keeps using memory after “freeing” it (i.e., after telling the operating system it’s done using it). This can lead to unpredictable results — at worst, allowing hackers to run their own code, crash the server, or steal data.

In CVE-2022-27457, the vulnerable part is inside the MariaDB source file:  
/strings/ctype-latin1.c, specifically the my_mb_wc_latin1 function, which handles certain string operations for the Latin1 character set.

1. Memory Management in MariaDB

The function my_mb_wc_latin1() should handle characters safely: allocate memory if needed, and avoid using memory that’s already been released.

2. The Vulnerable Pattern

In the buggy version, MariaDB code sometimes _frees_ memory after using it (say, by deleting a string buffer), but later reads or writes to that same freed chunk.

Here’s a simplified view of what might go wrong (not the full code, but an illustration)

char *buf = malloc(100);    // Allocate memory
strcpy(buf, "somedata");    // Use the buffer

free(buf);                  // Release memory

// ...some code and then
my_mb_wc_latin1(buf);       // Use-after-free: using buffer after it's been freed!

This is a classic UAF scenario, but in the real MariaDB code, it arises from more complex interactions inside string conversion and collation logic.

Part of the responsible code (simplified)

int my_mb_wc_latin1(...)
{
    ...
    /* use pointer (could be stale/freed) */
    *wc = (*src) & xff;
    ...
}

If the pointer src involves memory that was already freed elsewhere, reading from it can cause undefined behavior. An attacker may leverage heap grooming (arranging heap memory to specific patterns) to force a controlled crash or sometimes run arbitrary code.

Demonstration: Proof of Concept

To demonstrate the flaw, let's use a simplified C code snippet. This will simulate the use-after-free rather than use MariaDB’s internal structures — do not run this code on a production system!

Proof Of Concept (POC)

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

void my_mb_wc_latin1(char* src) {
    // Simulating vulnerable behavior
    printf("Output: %d\n", (*src) & xff);
}

int main() {
    char *ptr = (char *)malloc(8);
    strcpy(ptr, "A");

    free(ptr);  // Memory is freed, but pointer retained

    // Attacker can now try to overwrite freed memory here,

    my_mb_wc_latin1(ptr);  // UAF: using after freeing

    return ;
}

In real-world exploitation, attackers combine this bug with techniques that manipulate the memory allocator to overwrite the freed chunk with data they control.

Denial-of-Service (DoS): Crashing MariaDB server by causing invalid memory access.

- Arbitrary Code Execution: If other memory vulnerabilities exist or with sophisticated heap manipulation, running arbitrary code becomes possible.

Is There a Fix?

Yes. The MariaDB maintainers quickly patched the bug. Update to MariaDB v10.6.4 or newer to avoid this and similar issues. The fixed code ensures MariaDB doesn't read or write to freed memory.

See the security notice:

MariaDB Security Announcements

Patch details in code diff:

GitHub Commit Fix

Official CVE Entry:

NVD CVE-2022-27457

MariaDB Source File:

ctype-latin1.c

Further reading on UAF bugs:

What is Use-After-Free? (OWASP)

Conclusion

CVE-2022-27457 is a reminder that even mature, heavily relied-upon software like MariaDB can harbor critical vulnerabilities. Keep your systems patched, monitor for security advisories, and if you’re a developer, always be cautious with memory management — don’t use memory after you’ve freed it!

If you use MariaDB below v10.6.4, upgrade as soon as possible to protect your data and systems.

> Disclaimer: This writeup is for educational purposes only. Do not exploit vulnerable systems without full authorization.

Timeline

Published on: 04/14/2022 13:15:00 UTC
Last modified on: 06/30/2022 12:56:00 UTC