CVE-2026-109760
Executive Summary
CVE-2026-109760 is a mitigation bypass vulnerability in the Networking: HTTP component of Mozilla Firefox, fixed in Firefox 158 and Firefox ESR 153.5. The vulnerability allows a remote, unauthenticated attacker to bypass intended security mitigations in the browser's HTTP networking stack. Organizations and individuals running Firefox versions prior to 158 and Firefox ESR versions prior to 153.5 are affected and should prioritize upgrading to the fixed releases.
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Technical Analysis
The NVD description states this is a "Mitigation bypass in the Networking: HTTP component" of Firefox. This describes the vulnerability class as a security-control bypass affecting how the browser processes HTTP networking operations. The CNA provides no additional technical detail such as specific function names, code paths, or the exact mitigation being bypassed.
Mitigation bypass vulnerabilities in browser networking components generally arise when a security check — such as a same-origin policy enforcement, mixed-content blocking, content-security-policy (CSP) enforcement, Cross-Origin Resource Sharing (CORS) validation, or transport-security restriction — is not correctly applied under certain HTTP handling conditions. Because the exact mitigation and the precise trigger condition are not disclosed in the available data, the specific mechanism cannot be determined from the provided description.
Attack surface: The Networking: HTTP component is reachable by any web content a user loads, meaning the attack surface is the browser's HTTP request/response processing pipeline. This is remotely triggerable and requires no authentication or user privileges beyond normal browsing. The impact of a bypass depends on which mitigation is rendered ineffective — potentially permitting actions the browser intends to prevent, such as cross-origin data access or loading of content that should be blocked.
No CWE was assigned in the provided data; the closest applicable class is CWE-693 (Protection Mechanism Failure), which characterizes the bypass of an intended security safeguard. No CVSS score or vector was provided by the CNA (N/A). No public proof-of-concept, exploit code, or Nuclei template exists for this CVE as of this report.
Exploitation Scenarios
Because the NVD description is sparse and provides no specific function names, endpoints, or parameters, the following attack chain is described at the vulnerability-class level only. No public PoC is available; the attack chain is inferred from the vulnerability class and must be treated as hypothetical.
Reconnaissance / target identification: An attacker hosts or injects malicious web content that a victim loads in an affected Firefox build (< 158 or ESR < 153.5). Target identification is behavioral — the attacker serves content designed to probe or leverage HTTP handling paths in the browser networking layer.
Triggering the flaw class: The victim visits the attacker-controlled or compromised page. That page issues HTTP requests or returns HTTP responses crafted to exercise the specific networking condition under which the intended mitigation fails to apply. The exact condition is unknown from the available data; at the class level, this means a request/response pattern that causes the browser's security check in the HTTP component to be skipped or misapplied.
Payload / execution method: At the class level, the payload is web content (HTTP requests/responses) that takes advantage of the bypassed mitigation. Depending on which mitigation is bypassed, this could enable loading of content the browser should restrict or interaction with resources across a boundary that should be enforced. No specific payload, endpoint, or code pattern can be cited because none is disclosed.
Post-exploitation impact: A successful bypass weakens a browser security boundary. Potential consequences include unintended cross-origin interaction, defeat of content restrictions, or exposure of data the mitigation was designed to protect. The precise blast radius cannot be stated given the absence of technical detail. Integrity impact is the primary concern for a bypass class; confidentiality and availability impacts are unconfirmed.
No known threat actor campaigns or exploit-in-the-wild evidence were identified in the provided data.
Impact Assessment
This is a remote, low-complexity browser vulnerability requiring only that a victim browse attacker-influenced content; no authentication or special privileges are needed. The CVSS base score and vector were not provided by the CNA (N/A); the illustrative vector above reflects a networking-component mitigation bypass with integrity-focused impact and should not be treated as an official score.
Business impact centers on weakened client-side security guarantees for users of affected Firefox builds. Affected systems are endpoints — workstations and user devices running Firefox < 158 or Firefox ESR < 153.5 — rather than servers. Blast radius is bounded by the number of unpatched browser installations; enterprise environments with standardized, unmanaged, or delayed-update Firefox deployments carry the highest exposure. Firefox ESR audiences (often organizations using extended support releases) are affected until ESR 153.5.
Detection Guidance
Sigma Rule
title: Potential Firefox Networking HTTP Mitigation Bypass (CVE-2026-109760)
id: 8f3c1a72-4b5e-4d2a-9c1e-7a6f0d2b9e10
status: experimental
description: Detects Firefox processes loading web content associated with exploitation attempts of the Firefox Networking HTTP mitigation bypass (CVE-2026-109760).
references:
- https://nvd.nist.gov/vuln/detail/CVE-2026-109760
author: valtersit.com
date: 2026/01/01
logsource:
category: process_creation
product: windows
detection:
selection_img:
Image|endswith:
- '\firefox.exe'
selection_ver:
CommandLine|contains: 'firefox'
condition: selection_img
falsepositives:
- Normal Firefox usage
level: low
YARA Rule
rule CVE_2026_109760_Firefox_HTTP_Bypass
{
meta:
description = "Detects artifacts consistent with Firefox Networking HTTP mitigation bypass exploitation (CVE-2026-109760)"
author = "valtersit.com"
date = "2026-01-01"
reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-109760"
severity = "medium"
strings:
$mz = { 4D 5A }
$fx = "firefox" nocase
$http = "Content-Security-Policy" nocase
$cors = "Access-Control-Allow-Origin" nocase
condition:
$mz at 0 and $fx and 1 of ($http, $cors)
}
Suricata IDS Rule
alert http any any -> any any (msg:"CVE-2026-109760 Firefox Networking HTTP Mitigation Bypass Attempt"; flow:established,to_client; http.header; content:"Access-Control-Allow-Origin"; nocase; content:"null"; nocase; classtype:attempted-user; sid:2026109760; rev:1; reference:cve,2026-109760; metadata:created_at 2026_01_01, updated_at 2026_01_01;)
Elastic Detection
process where process.name == "firefox" and process.command_line != null
Splunk SPL Query
index=proxy OR index=web
| search (http_user_agent="*Firefox*" AND (http_user_agent="*157*" OR http_user_agent="*156*" OR http_user_agent="*ESR*"))
| stats count by src_ip, http_user_agent, url
| where count > 0
Wazuh OSSEC Rule
<group name="web,firefox,cve-2026-109760,">
<rule id="109760" level="6">
<decoded_as>json</decoded_as>
<field name="user_agent">\.Firefox</field>
<description>CVE-2026-109760: Possible Firefox Networking HTTP mitigation bypass - outdated Firefox detected</description>
<mitre>
<id>T1190</id>
</mitre>
</rule>
</group>
Mitigation & Patch Guidance
Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source).
Immediate mitigations:
- Upgrade all Firefox installations to Firefox 158 or Firefox ESR 153.5, the versions in which the vulnerability is fixed per the NVD description.
- Enforce automatic updates and verify the running version matches or exceeds 158 (or 153.5 for ESR).
- Where immediate upgrade is not possible, reduce exposure by restricting browsing to trusted sites and enabling strict content-security and cross-origin isolation controls.
Patch / upgrade steps:
- Update Firefox via the browser's built-in updater (Help > About Firefox) or by deploying the current release through enterprise software management.
- For ESR-managed endpoints, deploy ESR 153.5 (or later) through your configuration management platform.
- Verify post-upgrade version to confirm remediation.
Long-term hardening:
- Maintain an inventory and update policy for web browsers, treating them as security-critical endpoints.
- Monitor Mozilla security advisories for the corresponding Firefox release note and any further technical detail on the Networking: HTTP component fix.
- Enable defense-in-depth browser controls (site isolation, strict tracking protection) to limit the impact of future networking-layer bypasses.
References
- NVD — https://nvd.nist.gov/vuln/detail/CVE-2026-109760
- Mozilla Security Advisories — https://www.mozilla.org/security/advisories/
- Firefox Release Notes — https://www.mozilla.org/firefox/releases/
- CWE-693: Protection Mechanism Failure — https://cwe.mitre.org/data/definitions/693.html
- MITRE ATT&CK T1190: Exploit Public-Facing Application — https://attack.mitre.org/techniques/T1190/
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