CVE-2022-26485: Mozilla Firefox Use-After-Free Vulnerability

CVE-2022-26485 Overview

CVE-2022-26485 is a critical use-after-free vulnerability affecting Mozilla Firefox's XSLT (Extensible Stylesheet Language Transformations) processing engine. The flaw occurs when an XSLT parameter is removed during processing, leading to a dangling pointer condition that can be exploited by attackers to achieve arbitrary code execution. This vulnerability has been actively exploited in the wild, prompting emergency patches from Mozilla and inclusion in CISA's Known Exploited Vulnerabilities (KEV) catalog.

Critical Impact

This use-after-free vulnerability is actively exploited in the wild and enables remote code execution through malicious web content. CISA has added this CVE to its Known Exploited Vulnerabilities catalog, requiring immediate patching.

Affected Products

• Mozilla Firefox < 97.0.2
• Mozilla Firefox ESR < 91.6.1
• Mozilla Firefox for Android < 97.3.0
• Mozilla Thunderbird < 91.6.2
• Mozilla Firefox Focus < 97.3.0

Discovery Timeline

• 2022-12-22 - CVE-2022-26485 published to NVD
• 2025-11-04 - Last updated in NVD database

Technical Details for CVE-2022-26485

Vulnerability Analysis

This use-after-free vulnerability resides in Mozilla's XSLT processing implementation. XSLT is a language used to transform XML documents into other formats, and Mozilla browsers utilize this functionality to render web content. The vulnerability is triggered when an XSLT parameter is dynamically removed while the XSLT processor is still actively using it. This creates a use-after-free condition where the processor maintains a reference to memory that has already been deallocated.

The attack requires user interaction—specifically, a victim must navigate to or render malicious content containing a specially crafted XSLT stylesheet. Once triggered, the vulnerability allows attackers to corrupt memory and potentially hijack the execution flow of the browser process.

Root Cause

The root cause is improper memory management (CWE-416: Use After Free) in the XSLT parameter handling code. When XSLT parameters are modified during transformation processing, the code fails to properly synchronize parameter removal with active parameter references. This results in a dangling pointer that references freed memory, which can subsequently be reallocated and controlled by an attacker.

Attack Vector

Exploitation occurs via network-based attacks where a victim visits a malicious website or opens malicious content:

1. Initial Access: Attacker hosts or injects malicious XSLT content on a web page
2. Trigger Condition: Victim loads the page, initiating XSLT processing
3. Memory Corruption: The crafted XSLT triggers parameter removal during processing, creating a use-after-free condition
4. Code Execution: Attacker-controlled data fills the freed memory region, allowing arbitrary code execution within the browser context

The vulnerability is particularly dangerous because it can be triggered through normal web browsing without requiring additional plugins or user downloads. Mozilla has confirmed that attacks exploiting this flaw have been observed in the wild.

Detection Methods for CVE-2022-26485

Indicators of Compromise

• Unexpected browser crashes during web page loading, particularly pages with XML/XSLT content
• Suspicious outbound network connections from browser processes following page visits
• Memory corruption artifacts in browser crash dumps referencing XSLT transformation functions
• Unusual child process spawning from Firefox, Thunderbird, or Focus browser processes

Detection Strategies

• Deploy endpoint detection and response (EDR) solutions to monitor for anomalous browser behavior and memory exploitation attempts
• Implement network monitoring for connections to known malicious infrastructure associated with this exploit campaign
• Configure browser telemetry and crash reporting to identify potential exploitation attempts
• Review security logs for evidence of post-exploitation activity following browser process compromise

Monitoring Recommendations

• Enable enhanced security logging on endpoints running affected Mozilla products
• Monitor for updates to threat intelligence feeds regarding active exploitation campaigns targeting this vulnerability
• Implement application whitelisting to detect unauthorized code execution from browser processes
• Deploy SIEM rules to correlate browser crashes with subsequent suspicious activity

How to Mitigate CVE-2022-26485

Immediate Actions Required

• Update all Mozilla Firefox installations to version 97.0.2 or later immediately
• Update Mozilla Firefox ESR to version 91.6.1 or later
• Update Mozilla Thunderbird to version 91.6.2 or later
• Update Mozilla Firefox for Android and Firefox Focus to version 97.3.0 or later
• Prioritize patching based on CISA KEV listing requirements—federal agencies have mandatory remediation deadlines

Patch Information

Mozilla has released security patches addressing this vulnerability in emergency out-of-band updates. Detailed patch information is available in the Mozilla Security Advisory MFSA-2022-09. Technical details about the specific fix can be found in Mozilla Bug Report #1758062.

Organizations should deploy patches through their standard software update mechanisms. For enterprise environments, Mozilla provides ESR (Extended Support Release) versions with the security fix applied.

Workarounds

• Disable JavaScript temporarily to reduce attack surface (note: this significantly impacts web functionality)
• Use browser isolation solutions to contain potential exploitation in sandboxed environments
• Implement network-level filtering to block known malicious domains associated with this exploit
• Consider using alternative browsers temporarily until patches can be deployed in environments with slow update cycles
• Enable enhanced tracking protection and security features in Firefox to reduce exposure to malicious content

# Configuration example
# Verify Firefox version (ensure >= 97.0.2)
firefox --version

# For enterprise deployment, use policy files
# Create policies.json in Firefox installation directory
# /usr/lib/firefox/distribution/policies.json (Linux)
# C:\Program Files\Mozilla Firefox\distribution\policies.json (Windows)

cat << 'EOF' > /usr/lib/firefox/distribution/policies.json
{
  "policies": {
    "DisableAppUpdate": false,
    "AppAutoUpdate": true
  }
}
EOF