Mozilla Firefox and Thunderbird SVG Animation Use-After-Free Vulnerability (CVE-2016-9079) Technical Advisory
Executive & SecOps Summary
SECOPS ASSESSMENTFirefox < 50.0.2, Firefox ESR < 45.5.1, and Thunderbird < 45.5.1
Remote attackers can execute arbitrary code or cause memory corruption via crafted SVG animation elements, actively exploited in the wild against Tor and Firefox users
Immediately upgrade to Firefox 50.0.2+, Firefox ESR 45.5.1+, or Thunderbird 45.5.1+
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
For Linux-based endpoints, use the package manager to upgrade Firefox and Thunderbird to the latest secure versions.
# Update package repositories and upgrade applications
sudo apt-get update
sudo apt-get install --only-upgrade firefox thunderbird -y
# Verify the installed versions
firefox --version
thunderbird --version2. Temporary Workaround & Hardening Configuration
If immediate patching is not feasible, restrict JavaScript execution or enforce enterprise policies to block untrusted SVG rendering. Below is an example of configuring Firefox Enterprise Policies to mitigate the attack surface.
# Create or edit the enterprise policy file at /etc/firefox/policies/policies.json
cat << 'EOF' | sudo tee /etc/firefox/policies/policies.json
{
"policies": {
"DisableJavaScript": true,
"BlockAboutConfig": true
}
}
EOF3. Log Audit & IoC Verification Commands
Run the following shell script to audit local systems and identify vulnerable installations of Firefox.
#!/bin/bash
# Audit script to detect vulnerable Firefox installations
if command -v firefox >/dev/null 2>&1; then
INSTALLED_VER=$(firefox --version | awk '{print $3}')
SAFE_VER='50.0.2'
if [ '$(printf '%s\
' "$SAFE_VER" "$INSTALLED_VER" | sort -V | head -n1)' != "$SAFE_VER" ]; then
echo '[WARNING] Vulnerable Firefox version detected: '$INSTALLED_VER
else
echo '[OK] Firefox version is secure: '$INSTALLED_VER
fi
else
echo '[INFO] Firefox is not installed on this system.'
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Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
A critical Use-After-Free (UAF) vulnerability (CVE-2016-9079) exists within the SVG Animation engine of Mozilla Firefox and related products. The root cause lies in the improper lifecycle management of DOM objects during the parsing and rendering of SVG elements. When a specific SVG animation object is deleted from memory, the pointer referencing it is not cleared, leading to a dangling pointer that can be subsequently accessed.
2. Exploitation Mechanics & Attack Scenario
An attacker exploits this vulnerability by hosting a malicious web page containing specifically crafted SVG animation tags. When a vulnerable browser renders the page, JavaScript is typically used to manipulate the heap layout, forcing the destruction and reallocation of the target SVG elements. By filling the freed memory space with attacker-controlled data, the subsequent reuse of the dangling pointer triggers arbitrary code execution within the context of the browser process.
3. Infrastructure & Business Impact
This vulnerability was actively exploited in the wild as a zero-day targeting Windows users of Firefox and the Tor Browser to bypass anonymity protections. Given its inclusion in the CISA KEV catalog and high EPSS score, successful exploitation poses a severe threat to enterprise endpoints, potentially allowing initial access, credential theft, and lateral movement within corporate networks.
Official Vendor Advisories & References
A use-after-free vulnerability in SVG Animation has been discovered. An exploit built on this vulnerability has been discovered in the wild targeting Firefox and Tor Browser users on Windows. This vulnerability affects Firefox < 50.0.2, Firefox ESR < 45.5.1, and Thunderbird < 45.5.1.
Frequently Asked SecOps Questions (CVE-2016-9079)
FAQQ1. How critical is CVE-2016-9079 and is it actively exploited in the wild?
CVE-2016-9079 is rated CVSS 7.5 (HIGH) with a 30-day EPSS exploitation probability of 87.4%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2016-9079?
Primary impacted vendors include mozilla across firefox, firefox_esr, thunderbird. Scope summary: Firefox versions prior to 50.0.2, Firefox ESR versions prior to 45.5.1, and Thunderbird versions prior to 45.5.1 across all operating systems
Q3. What temporary mitigations or workarounds exist for CVE-2016-9079 before patching?
[Mitigation] Immediately upgrade to Firefox 50.0.2+, Firefox ESR 45.5.1+, or Thunderbird 45.5.1+ Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
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