CVE-2026-109713

Executive Summary

CVE-2026-109713 is a use-after-free vulnerability in the Crash Reporting component of Mozilla Firefox. Successful exploitation requires user interaction, such as visiting a crafted web page, and could lead to arbitrary code execution or a denial-of-service condition. All Firefox users running versions prior to 158 and Firefox ESR users prior to 153.5 are affected.

Technical Analysis

The vulnerability resides in Firefox's Crash Reporting component, which handles the collection, storage, and submission of crash data to Mozilla. A use-after-free (UAF) condition occurs when a program continues to reference memory after it has been freed. In the context of crash reporting, this could manifest when crash metadata, minidump structures, or associated objects are released prematurely while still being accessed by another part of the crash-handling pipeline.

The attack surface for this issue involves the browser's internal crash reporting mechanisms. Because the Crash Reporting component operates in both content and parent processes, a UAF here could potentially be triggered through crafted web content that induces a crash in a specific manner, causing the browser to mishandle the subsequent crash-reporting lifecycle. The exact trigger conditions (specific object lifecycle, memory layout, and crash type required) are not detailed in the available NVD description. No CWE has been assigned beyond the implied CWE-416 (Use After Free) based on the vulnerability class.

Key facts:

• Vulnerability class: Use-after-free (CWE-416)
• Component: Crash Reporting
• Fixed in: Firefox 158, Firefox ESR 153.5
• Attack vector: Network (via web content), requires user interaction
• Impact: Potential arbitrary code execution in the browser process context, or denial of service

Insufficient technical detail is available in the NVD description to identify specific function names, freed object types, or the exact lifetime bug. The report therefore remains at the vulnerability-class level.

Exploitation Scenarios

1. Reconnaissance/target identification: An attacker identifies targets running a vulnerable version of Firefox. This could be done through browser fingerprinting, User-Agent strings, or malformed JavaScript probing. Shodan dorks such as http.html:"Crash Reporter" could identify exposed instances of the crash reporting interface, though this is less relevant for client-side exploitation.

2. Triggering the flaw: The attacker crafts a malicious web page that causes the browser to initiate a crash reporting sequence in a way that triggers the use-after-free. This likely involves inducing a specific type of crash (or triggering the crash reporter's UI/submission flow) while a particular object is freed and then reused. The exact JavaScript or HTML pattern required is not described in the available intelligence.

3. Payload/execution method: At the vulnerability-class level, a UAF in a browser component typically allows heap grooming and subsequent control-flow hijacking. The attacker would need to arrange heap memory such that the freed object is reallocated with attacker-controlled data, and then trigger a virtual call or function pointer dereference through the stale reference. No public PoC is available; the attack chain is inferred from the vulnerability class.

4. Post-exploitation impact: Successful exploitation could result in arbitrary code execution within the Firefox process sandbox. Depending on sandbox escape primitives (not described here), this could lead to full system compromise. In less severe cases, it would cause a crash (denial of service) of the browser.

Impact Assessment

A use-after-free in a core browser component like Crash Reporting is serious. If exploited, an attacker can achieve remote code execution in the context of the Firefox process. However, the requirement for user interaction (visiting a malicious page) somewhat narrows the attack surface from a "no-click" perspective. The CVSS vector (AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H) indicates:

• Confidentiality: High — potential theft of sensitive data from the browser.
• Integrity: High — arbitrary code execution can modify system state.
• Availability: High — crash or arbitrary code can disrupt service.
• Scope: Unchanged — the vulnerable component and impacted component are the same (Firefox process).

Affected systems include all desktop and mobile Firefox deployments prior to 158, and ESR deployments prior to 153.5. Given Firefox's significant enterprise and consumer footprint, the blast radius is large. However, no active exploitation in the wild has been reported, and no CISA KEV listing exists.

Detection Guidance

Sigma Rule

title: Potential Firefox Crash Reporting Use-After-Free Exploitation
status: experimental
description: Detects potential exploitation attempts of CVE-2026-109713 via unusual crash reporter activity
author: Threat Intelligence
date: 2026-01-01
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith:
            - '\firefox.exe'
            - '\crashreporter.exe'
        CommandLine|contains:
            - 'crashreporter'
            - '-greomni'
            - '-appdata'
    condition: selection
fields:
    - CommandLine
    - ParentImage
falsepositives:
    - Legitimate browser crashes
level: medium
tags:
    - attack.t1203
    - cve.2026.109713

YARA Rule

rule CVE_2026_109713_Firefox_CrashReporter_UAF
{
    meta:
        description = "Detects potential exploit artifacts for CVE-2026-109713 in memory or crash dumps"
        author = "Threat Intelligence"
        date = "2026-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-109713"
        severity = "high"

    strings:
        $crash1 = "CrashReporter" ascii wide nocase
        $crash2 = "minidump" ascii wide nocase
        $ff1 = "firefox" ascii wide nocase
        $heap_spray = { 0C 0C 0C 0C 0C 0C 0C 0C } // common heap spray pattern, adjust as needed
        $uaf_marker = "UseAfterFree" ascii wide nocase

    condition:
        (uint16(0) == 0x5A4D or uint32(0) == 0x464C457F) and // PE or ELF
        filesize < 20MB and
        (
            (2 of ($crash*) and 1 of ($ff1)) or
            ($uaf_marker and 1 of ($crash*)) or
            ($heap_spray and 2 of ($crash*))
        )
}

Suricata IDS Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"Potential Firefox Crash Reporting Use-After-Free Exploitation Attempt (CVE-2026-109713)"; flow:to_server,established; content:"CrashReporter"; http_user_agent; nocase; content:"Firefox/"; http_user_agent; distance:0; nocase; pcre:"/Firefox\/(1[0-4][0-9]|15[0-7])/"; metadata:service http; reference:cve,2026-109713; classtype:attempted-user; sid:10000001; rev:1;)

Elastic Detection

process where event.type == "start" and
process.name : ("firefox.exe", "crashreporter.exe") and
process.command_line : "*crashreporter*" and
process.parent.name : "firefox.exe"

Splunk SPL Query

index=main sourcetype=WinEventLog:Security OR sourcetype=XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
(EventID=1 OR EventCode=1)
(Image="*\\firefox.exe" OR Image="*\\crashreporter.exe")
(CommandLine="*crashreporter*" OR CommandLine="*-greomni*")
| stats count values(CommandLine) by Computer, User, Image
| where count > 5

Wazuh OSSEC Rule

<group name="firefox,cve-2026-109713,">
  <rule id="100200" level="10">
    <decoded_as>json</decoded_as>
    <field name="win.eventdata.image">\.exe$</field>
    <field name="win.eventdata.image">firefox\.exe|crashreporter\.exe</field>
    <field name="win.eventdata.commandLine">crashreporter|-greomni</field>
    <description>Possible exploitation attempt of CVE-2026-109713 (Firefox Crash Reporting UAF)</description>
    <mitre>
      <id>T1203</id>
    </mitre>
    <group>exploit_attempts,</group>
  </rule>
</group>

Mitigation & Patch Guidance

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

Immediate mitigations:

• Disable or restrict JavaScript execution via browser settings or policy where feasible.
• Use browser isolation technologies or sandboxing to contain potential exploits.
• Deploy network-level detection rules (Suricata, etc.) to alert on suspicious crash reporting activity.
• Ensure users are trained to avoid suspicious or untrusted web pages.

Patch/upgrade steps:

• The vulnerability is fixed in Firefox 158 and Firefox ESR 153.5. Organizations should upgrade to these versions or later immediately.
• For enterprise deployments, use Firefox's built-in update mechanisms or package managers to push the update.
• Verify the installed version through about:support or command-line firefox --version.

Long-term hardening:

• Enable automatic updates for Firefox and other browsers to ensure timely patching.
• Adopt a vulnerability management program that tracks browser CVEs and applies patches within defined SLAs.
• Consider using browser hardening guides (e.g., CIS benchmarks) to reduce attack surface.
• Monitor for future Firefox security advisories and maintain a rapid response capability.

References

• NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-109713
• Mozilla Security Advisories: https://www.mozilla.org/en-US/security/advisories/
• Mozilla Foundation Security Advisory (Firefox 158/ESR 153.5) — refer to official release notes
• CWE-416: Use After Free — https://cwe.mitre.org/data/definitions/416.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 have been identified for this CVE at the time of writing.