CVE-2022-43552: Haxx Curl Use After Free Vulnerability

CVE-2022-43552 Overview

A use after free vulnerability exists in curl versions prior to 7.87.0. Curl can be configured to tunnel virtually all protocols it supports through an HTTP proxy. HTTP proxies can (and often do) deny such tunnel operations. When getting denied to tunnel the specific protocols SMB or TELNET, curl would use a heap-allocated struct after it had been freed in its transfer shutdown code path.

Critical Impact

This use after free vulnerability can lead to denial of service conditions when curl attempts to tunnel SMB or TELNET protocols through an HTTP proxy that denies the connection request.

Affected Products

• Haxx curl (versions prior to 7.87.0)
• Apple macOS (multiple versions)
• Splunk Universal Forwarder (including version 9.1.0)

Discovery Timeline

• 2023-02-09 - CVE CVE-2022-43552 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-43552

Vulnerability Analysis

This vulnerability is classified as CWE-416 (Use After Free), a critical memory corruption issue that occurs when a program continues to use a pointer after the memory it references has been deallocated. In the context of curl, this manifests specifically during the transfer shutdown code path when handling proxy tunnel denials.

The vulnerability requires specific conditions to trigger: the application must be configured to tunnel either SMB or TELNET protocols through an HTTP proxy, and that proxy must actively deny the tunnel request. When these conditions are met, curl accesses a heap-allocated structure that has already been freed during the connection cleanup process.

While exploitation requires a high attack complexity (the attacker would need to control or influence the HTTP proxy behavior), successful exploitation could result in application crashes or potentially more severe memory corruption scenarios depending on heap state.

Root Cause

The root cause lies in improper memory management within curl's transfer shutdown code path. When an HTTP proxy denies a tunnel request for SMB or TELNET protocols, the shutdown routine frees memory associated with the connection. However, subsequent code in the same execution path incorrectly references this freed memory structure.

This is a classic use after free pattern where the lifecycle of a heap-allocated object is not properly synchronized with all code paths that reference it. The fix requires ensuring the memory is either not freed until all references are complete, or that references are nullified immediately after freeing.

Attack Vector

The attack vector is network-based, requiring the attacker to either:

1. Control an HTTP proxy that the vulnerable curl client is configured to use
2. Perform a man-in-the-middle attack to intercept and modify proxy responses
3. Configure a malicious proxy and social engineer the victim into using it

When the attacker-controlled proxy denies tunnel requests for SMB or TELNET protocols, it triggers the vulnerable code path in curl's connection handling. The attack does not require any user interaction beyond the initial connection attempt, and no privileges are required on the target system.

The vulnerability mechanism involves the following sequence: When curl initiates a tunnel request through an HTTP proxy for SMB or TELNET protocols, the proxy can respond with a denial. During the processing of this denial in the transfer shutdown code, curl accesses heap memory that has already been deallocated. This can lead to crashes or unpredictable behavior depending on whether the freed memory has been reallocated for other purposes.

Detection Methods for CVE-2022-43552

Indicators of Compromise

• Unexpected curl process crashes when connecting through HTTP proxies
• Core dumps or crash logs showing memory access violations in curl's transfer handling code
• Application logs indicating failed SMB or TELNET tunnel attempts followed by crashes
• Memory corruption errors in applications embedding libcurl

Detection Strategies

• Monitor for curl process crashes or segmentation faults, particularly when HTTP proxy configurations are in use
• Implement network monitoring to detect SMB or TELNET tunnel attempts through HTTP proxies
• Use memory debugging tools (such as Valgrind or AddressSanitizer) in development environments to detect use after free conditions
• Review application logs for patterns indicating proxy tunnel denials followed by unexpected terminations

Monitoring Recommendations

• Deploy endpoint detection and response (EDR) solutions to monitor curl-based application behavior
• Implement network traffic analysis to identify anomalous proxy tunnel request patterns
• Enable crash dump collection and analysis for applications using curl or libcurl
• Monitor system event logs for application faults related to curl components

How to Mitigate CVE-2022-43552

Immediate Actions Required

• Upgrade curl to version 7.87.0 or later immediately
• Update Apple macOS to the latest patched version (see Apple Support Article HT213670)
• Update Splunk Universal Forwarder to a patched version
• Audit systems for curl versions and create an inventory of affected deployments

Patch Information

The vulnerability has been addressed in curl version 7.87.0 and later releases. Multiple vendors have released patches for products that bundle curl:

• Haxx curl: Fixed in version 7.87.0 - Details available via the HackerOne Report #1764858
• Apple macOS: Security update available - See Apple Support Article HT213670
• Splunk Universal Forwarder: Update to latest patched version
• NetApp Products: See NetApp Security Advisory for affected products
• Gentoo Linux: See Gentoo GLSA 202310-12 for update instructions

Workarounds

• Avoid tunneling SMB or TELNET protocols through HTTP proxies until patching is complete
• Configure network policies to block SMB and TELNET tunnel attempts through HTTP proxies at the network perimeter
• Implement application-level controls to prevent curl from attempting SMB or TELNET proxy tunneling
• Consider using alternative protocols that do not trigger the vulnerable code path

# Check installed curl version
curl --version

# Verify curl is updated to patched version (7.87.0 or later)
curl -V | grep -E "curl [0-9]+\.[0-9]+\.[0-9]+"

# For systems using package managers, update curl
# Debian/Ubuntu:
apt-get update && apt-get upgrade curl

# RHEL/CentOS:
yum update curl

# macOS (using Homebrew):
brew upgrade curl