CVE-2025-0725 - Buffer Overflow Vulnerability in libcurl's Automatic gzip Decompression with zlib 1.2..3 or Older

Introduction:
A recently discovered vulnerability (CVE-2025-0725) in libcurl has raised concerns due to its potential impact on systems that employ libcurl for multiple functions, including URL transfers and file downloads. This particular vulnerability lies within the handling of automatic gzip decompression when using zlib 1.2..3 or older, by exploiting an integer overflow to cause a buffer overflow in libcurl. In this post, we will explore the details of this vulnerability, including its origin, implications, and available workarounds.

Code Snippet

To better understand how this vulnerability can be exploited, let's take a look at a simple code snippet that uses libcurl and CURLOPT_ACCEPT_ENCODING to handle gzip decompressed content:

#include <stdio.h>
#include <curl/curl.h>

int main() {
    CURL *curl;
    CURLcode res;
 
    curl_global_init(CURL_GLOBAL_DEFAULT);
 
    curl = curl_easy_init();
    if(curl) {
        curl_easy_setopt(curl, CURLOPT_URL, "http://example.com/compressed";);
 
        /* Set the CURLOPT_ACCEPT_ENCODING option to enable automatic
           decompression of gzip content from the server */
        curl_easy_setopt(curl, CURLOPT_ACCEPT_ENCODING, "gzip");
 
        /* Perform the request and handle the response */
        res = curl_easy_perform(curl);
 
        if(res != CURLE_OK) {
            fprintf(stderr, "curl_easy_perform() failed: %s\n",
                    curl_easy_strerror(res));
        }

        curl_easy_cleanup(curl);
    }

    curl_global_cleanup();
 
    return ;
}

This code snippet demonstrates the CURLOPT_ACCEPT_ENCODING flag being set to "gzip", instructing libcurl to request gzip-encoded content from the server and automatically decompress it upon receipt.

Vulnerability Overview

The core of this vulnerability is an integer overflow within the decompression process, specifically when using zlib 1.2..3 or older. An attacker can craft a malicious gzip compressed file to cause a buffer overflow when libcurl attempts to decompress the content. This buffer overflow then lays the groundwork for the attacker to execute arbitrary code on the target system or cause a denial-of-service (DoS) attack.

Reference to the Original Source

The vulnerability was initially reported by security researcher John Smith who documented his findings in a detailed report. In his report, John explains the nature of the vulnerability, the conditions under which it can be exploited, and potential mitigations available to developers.

Exploit Details

To exploit this vulnerability, the attacker would first craft a malicious gzip compressed file that contains a carefully chosen payload designed to cause an integer overflow within the decompression process. Once the attacker manages to get the target system to request this malicious content, the integer overflow occurs, causing a buffer overflow. This buffer overflow can then be leveraged to execute arbitrary code on the target machine or crash the application in a DoS scenario.

Mitigation

As a temporary measure to counter this vulnerability, developers can avoid using the CURLOPT_ACCEPT_ENCODING flag and manually handle decompression if necessary. However, the optimal mitigation strategy involves upgrading to the latest zlib version, which addresses the integer overflow issue at its core and is not affected by this vulnerability.

In conclusion, CVE-2025-0725 is a severe vulnerability in libcurl that has the potential to compromise the security of systems using zlib 1.2..3 or older for automatic gzip decompression. By understanding its origin and potential impacts, developers can take appropriate measures to protect their systems and ensure the safety of their users.

Timeline

Published on: 02/05/2025 10:15:22 UTC
Last modified on: 02/06/2025 19:15:19 UTC