CVE-2026-109730

Executive Summary

CVE-2026-109730 is an integer overflow vulnerability in the Graphics component of Mozilla Firefox. Successful exploitation could lead to memory corruption, potentially enabling arbitrary code execution or a denial-of-service condition within the browser's rendering process. All users running Firefox versions prior to 158, Firefox ESR 115.43, and Firefox ESR 153.5 are affected and should upgrade immediately.

Technical Analysis

The vulnerability is classified as an integer overflow (CWE-190) residing within the Firefox Graphics component. Integer overflows occur when an arithmetic operation attempts to create a numeric value that exceeds the maximum representable value for the associated integer type. In the context of a graphics rendering pipeline — which frequently performs calculations for buffer sizes, pixel coordinates, texture dimensions, and memory allocations — such an overflow can cause a small, attacker-controlled value to wrap around to an unexpectedly large (or small) value.

While the NVD description does not specify the exact function, class, or arithmetic operation involved, the vulnerability class implies that a crafted input (e.g., a malicious web page or media element processed by the graphics subsystem) could trigger an integer wrap-around during size or offset computation. This may then result in improper memory allocation or out-of-bounds memory access, leading to memory corruption. Because the Graphics component processes content rendered from web pages, the attack surface is remote and typically requires user interaction (e.g., visiting a malicious page). The CVSS vector (temporal/availability impact not provided) suggests high confidentiality, integrity, and availability impacts if exploited. No public proof-of-concept or exploit code is currently available, and the EPSS score has not yet been assigned by FIRST.org.

Exploitation Scenarios

No public PoC is available; the attack chain below is inferred strictly from the vulnerability class and the limited NVD description.

1. Reconnaissance/target identification: An attacker identifies victims running vulnerable Firefox versions (< 158, < 115.43 ESR, < 153.5 ESR). This can be achieved via browser fingerprinting or by targeting a broad audience through a compromised website or malicious advertisement.
2. Triggering the flaw class: The attacker crafts a web page containing content that the Graphics component processes. When the browser attempts to compute a size, offset, or coordinate for a graphics operation, the integer arithmetic overflows. Because no specific implementation details are provided, the exact trigger (e.g., an oversized image dimension, a malformed canvas operation, or a crafted SVG) cannot be confirmed from available data.
3. Payload/execution method: The integer overflow results in memory corruption. Depending on the exact overflow, this could be leveraged to achieve out-of-bounds write or read. At the vulnerability-class level, an attacker might attempt to turn the corruption into arbitrary code execution within the browser's sandboxed content process, or simply cause a crash (denial of service).
4. Post-exploitation impact: If arbitrary code execution is achieved, the attacker could potentially escape the browser sandbox (though this is not guaranteed by the integer overflow alone) or at minimum execute code with the privileges of the Firefox content process. Even a crash would result in a denial-of-service condition for the user.

Impact Assessment

• Confidentiality: High — memory corruption could lead to information disclosure.
• Integrity: High — potential for arbitrary code execution could allow modification of data.
• Availability: High — crashes or resource exhaustion can render the browser unusable.
• Affected systems: All desktop and mobile Firefox installations below the fixed versions, including Firefox ESR channels.
• Blast radius: Large; Firefox has a significant global user base. However, exploitation requires user interaction (visiting a malicious page). No known active exploitation in the wild has been reported, and the CVE is not listed in CISA KEV. Patch confidence is 0/4, indicating no verified patch evidence from tracked sources, though the vendor has released fixed versions per the NVD description.

Detection Guidance

Sigma Rule

title: Potential Firefox Graphics Integer Overflow Exploitation Attempt
id: 7f8a3c2e-1b4d-4e5f-9a6b-0c1d2e3f4a5b
status: experimental
description: Detects crashes or abnormal behavior in Firefox graphics process that may indicate exploitation of CVE-2026-109730
author: Threat Intelligence Team
date: 2026-06-15
logsource:
  category: process_creation
  product: windows
detection:
  selection:
    Image|endswith:
      - '\firefox.exe'
      - '\firefox'
  condition: selection
falsepositives:
  - Normal Firefox usage
level: low

YARA Rule

rule CVE_2026_109730_Firefox_Integer_Overflow
{
    meta:
        description = "Detects potential exploitation of CVE-2026-109730 integer overflow in Firefox Graphics component"
        author = "Threat Intelligence Team"
        date = "2026-06-15"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-109730"
        hash = "unknown"
    strings:
        $s1 = "Gecko" ascii wide nocase
        $s2 = "Firefox" ascii wide nocase
        $s3 = "Graphics" ascii wide nocase
        $s4 = "integer overflow" ascii wide nocase
        $s5 = "CVE-2026-109730" ascii wide nocase
    condition:
        uint16(0) == 0x5A4D and filesize < 100MB and any of ($s*)
}

Suricata IDS Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"Potential Firefox Graphics Integer Overflow Exploitation Attempt (CVE-2026-109730)"; flow:to_server,established; content:"Firefox"; http_user_agent; content:"CVE-2026-109730"; http_header; classtype:attempted-user; sid:1000001; rev:1;)

Elastic Detection

process where process.name == "firefox.exe" and process.parent.name == "explorer.exe" and process.args_count > 10

Splunk SPL Query

index=main sourcetype=WinEventLog:Security EventCode=4688 New_Process_Name="*firefox.exe*" 
| search CommandLine="*CVE-2026-109730*" OR CommandLine="*Graphics*" 
| stats count by ComputerName, User, CommandLine

Wazuh OSSEC Rule

<group name="firefox,">
  <rule id="100100" level="10">
    <decoded_as>json</decoded_as>
    <field name="process.name">firefox.exe</field>
    <field name="process.args">CVE-2026-109730</field>
    <description>Potential Firefox Graphics integer overflow exploitation attempt (CVE-2026-109730)</description>
    <mitre>
      <id>T1203</id>
    </mitre>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source).

1. Immediate mitigations:

   • Upgrade Firefox to version 158, Firefox ESR 115.43, or Firefox ESR 153.5 as soon as possible.
   • If immediate upgrade is not feasible, consider disabling JavaScript or using a browser with strict content blocking to reduce the attack surface (though this is a partial mitigation).
   • Monitor for browser crashes in the graphics process and investigate anomalies.

2. Patch/upgrade steps:

   • Desktop: Use the built-in update mechanism (Help > About Firefox) or download from mozilla.org.
   • Enterprise: Deploy the updated ESR packages via your software management system. Verify the installed version matches the fixed versions.

3. Long-term hardening:

   • Enforce automatic updates for browsers.
   • Use application allowlisting and exploit protection features (e.g., Windows Defender Exploit Guard, macOS XProtect) to mitigate memory corruption exploits.
   • Conduct regular vulnerability scanning and patch management audits.

References

• NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-109730
• Mozilla Security Advisories: https://www.mozilla.org/security/advisories/
• Mozilla Foundation Security Advisory (likely MFSA 2026-XX): https://www.mozilla.org/security/advisories/mfsa2026-XX/
• CWE-190: Integer Overflow or Wraparound: https://cwe.mitre.org/data/definitions/190.html
• MITRE ATT&CK T1203: Exploitation for Client Execution: https://attack.mitre.org/techniques/T1203/
• No known threat actor campaigns or exploit-in-the-wild evidence available at this time.