Curl 7.84 = 8.2.1 Header DoS (CVE‐2023‐38039)

Overview

Curl is a command-line tool and library for transferring data with URLs. Versions 7.84 through 8.2.1 are vulnerable to a Denial of Service (DoS) attack, specifically a header-based DoS, identified as CVE-2023-38039. This vulnerability can cause the application to crash or consume excessive resources when processing specially crafted headers.

• Severity: High

Impact

• Application Crash: Exploiting this vulnerability can crash Curl, leading to denial of service.
• Resource Exhaustion: Maliciously crafted headers can cause Curl to consume excessive CPU or memory resources.
• Service Disruption: Continuous exploitation can lead to prolonged unavailability of services relying on Curl.

Cause

• Improper Header Parsing: Vulnerabilities in the way Curl parses and handles headers can lead to crashes or resource exhaustion.
• Memory Management Issues: Flaws in memory allocation and deallocation when processing headers.
• Lack of Input Validation: Inadequate validation of incoming headers can allow malformed headers to exploit the vulnerability.

Solution

1. Update Curl:

   • Update Curl to version 8.2.2 or later, where this vulnerability has been patched.

     sudo apt-get update
     sudo apt-get install curl

2. Implement Input Validation:

   • Validate and sanitize headers before processing them with Curl to reduce the risk of exploitation.

3. Resource Limits:

   • Configure resource limits for applications using Curl to prevent resource exhaustion.

     ulimit -v 1048576  # Set a limit of 1GB of virtual memory

Examples

Practical Example - CVE-2023-38039

# Example script to exploit the header-based DoS vulnerability in Curl
curl -v -H "$(python3 -c 'print("A" * 10000)')" http://example.com

This example shows how an excessively long header can be used to exploit the vulnerability in Curl, potentially leading to a crash or resource exhaustion.

Updating Curl

1. For Ubuntu/Debian:

sudo apt-get update
sudo apt-get install curl

2. For Red Hat/CentOS:

sudo yum update
sudo yum install curl

References

• Curl Security Advisories
• Keeping Curl Safe

Additional Resources

N/A