CVE-2023-37202: Mozilla Firefox Use-After-Free Vulnerability

CVE-2023-37202 Overview

CVE-2023-37202 is a use-after-free vulnerability affecting Mozilla Firefox, Firefox ESR, and Thunderbird. The flaw exists in how cross-compartment wrappers handle scripted proxies, potentially allowing objects from other compartments to be incorrectly stored in the main compartment. This memory management issue can lead to a use-after-free condition when the referenced memory is accessed after being freed, potentially enabling arbitrary code execution in the context of the browser.

Critical Impact

Successful exploitation of this use-after-free vulnerability could allow an attacker to execute arbitrary code, potentially leading to complete system compromise if a user visits a maliciously crafted webpage.

Affected Products

• Mozilla Firefox versions prior to 115
• Mozilla Firefox ESR versions prior to 102.13
• Mozilla Thunderbird versions prior to 102.13
• Debian Linux 10.0, 11.0, and 12.0 (via bundled Firefox/Thunderbird packages)

Discovery Timeline

• July 5, 2023 - CVE-2023-37202 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2023-37202

Vulnerability Analysis

This vulnerability is classified as CWE-416 (Use After Free), a memory corruption issue that occurs when a program continues to use a pointer after the memory it references has been freed. In the context of Mozilla's JavaScript engine, the vulnerability manifests in the handling of cross-compartment wrappers when they wrap scripted proxy objects.

Mozilla's SpiderMonkey JavaScript engine uses compartments to isolate different security contexts and origins. Cross-compartment wrappers (CCWs) serve as intermediaries that allow controlled access to objects in different compartments while maintaining security boundaries. When a CCW wraps a scripted proxy—a JavaScript Proxy object with custom handlers—the interaction can cause objects from other compartments to be stored in the main compartment unexpectedly.

This incorrect storage can lead to premature garbage collection of the referenced objects while pointers to them remain active. When these dangling pointers are subsequently dereferenced, the use-after-free condition occurs, potentially allowing an attacker to manipulate program execution flow.

Root Cause

The root cause lies in the improper handling of compartment boundaries when cross-compartment wrappers interact with scripted proxy objects. The JavaScript engine fails to correctly track object ownership and lifetime when proxy handlers operate across compartment boundaries, resulting in objects being stored in incorrect compartments. This violates the invariants expected by the garbage collector, leading to premature deallocation of memory that is still referenced.

Attack Vector

The attack vector for CVE-2023-37202 is network-based and requires user interaction. An attacker would need to craft a malicious webpage containing JavaScript code that exploits the cross-compartment wrapper behavior with scripted proxies. When a victim visits the malicious page using an affected browser version, the JavaScript executes in the browser context, triggering the use-after-free condition.

The vulnerability mechanism involves creating scripted proxy objects and manipulating cross-compartment wrapper interactions to cause improper object storage. Technical details are available in Mozilla Bug Report #1834711. Exploitation would typically involve heap manipulation techniques to control the contents of freed memory, potentially allowing the attacker to hijack program control flow and achieve arbitrary code execution.

Detection Methods for CVE-2023-37202

Indicators of Compromise

• Unexpected browser crashes or instability when visiting unknown websites
• Memory corruption errors or access violations in Firefox, Firefox ESR, or Thunderbird processes
• Unusual JavaScript execution patterns involving Proxy objects in browser memory dumps
• Child processes spawned from browser with unexpected network connections or file access

Detection Strategies

• Monitor browser processes for abnormal memory access patterns or crash signatures consistent with use-after-free exploitation
• Implement network-based detection for web pages serving heavily obfuscated JavaScript with Proxy object instantiation patterns
• Deploy endpoint detection rules that identify suspicious process spawning from Firefox or Thunderbird parent processes
• Utilize browser telemetry and crash reports to identify potential exploitation attempts

Monitoring Recommendations

• Enable enhanced crash reporting in Mozilla products to capture detailed memory state during failures
• Configure SentinelOne agents to monitor for suspicious behavior originating from browser processes
• Implement web proxy logging to identify and investigate visits to suspicious domains preceding browser anomalies
• Review browser extension activity for unauthorized modifications that could facilitate exploitation

How to Mitigate CVE-2023-37202

Immediate Actions Required

• Update Mozilla Firefox to version 115 or later immediately
• Update Mozilla Firefox ESR to version 102.13 or later
• Update Mozilla Thunderbird to version 102.13 or later
• Apply Debian security updates if running affected Debian Linux versions (10.0, 11.0, or 12.0)

Patch Information

Mozilla has released security patches addressing this vulnerability across all affected products. The fixes are documented in the following security advisories:

• Mozilla Security Advisory MFSA-2023-22 - Firefox 115
• Mozilla Security Advisory MFSA-2023-23 - Firefox ESR 102.13
• Mozilla Security Advisory MFSA-2023-24 - Thunderbird 102.13

Debian users should apply the updates from DSA-5450 and DSA-5451.

Workarounds

• Disable JavaScript execution in the browser temporarily if immediate patching is not possible (note: this will significantly impact web functionality)
• Use browser isolation technologies to contain potential exploitation within sandboxed environments
• Restrict browsing to trusted websites only until patches can be applied
• Consider using an alternative browser temporarily while updates are being deployed across the organization

# Verify Firefox version on Linux systems
firefox --version

# Verify Thunderbird version
thunderbird --version

# Update Firefox via package manager (Debian/Ubuntu)
sudo apt update && sudo apt upgrade firefox-esr

# Update Thunderbird via package manager (Debian/Ubuntu)
sudo apt update && sudo apt upgrade thunderbird