CVE-2026-119425
Received Received - Intake

Authentication Bypass in OPNsense Captive Portal

Publication date: 2026-10-30

Last updated on: 2026-10-30

Assigner: VulnCheck

Description
OPNsense core 26.1.6 through 26.7.7 contains an authentication bypass vulnerability in the captive portal roaming feature that lets unauthenticated attackers hijack authorized client sessions by spoofing unauthenticated MAC-to-IP observations. Attackers on the same Layer-2 segment can send forged gratuitous ARP replies binding their IP to a victim's MAC, gaining portal access with traffic attributed to the victim.

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Meta Information

Published
2026-10-30
Last Modified
2026-10-30
Generated
2026-10-30
AI Q&A
2026-10-30
EPSS Evaluated
N/A
NVD
CVE-2026-119425
EUVD
EUVD-2026-113805

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
opnsense core 26.1.6

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-290 This attack-focused weakness is caused by incorrectly implemented authentication schemes that are subject to spoofing attacks.

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Executive Summary

This vulnerability is an authentication bypass in OPNsense core versions 26.1.6 through 26.7.7. It affects the captive portal roaming feature, allowing unauthenticated attackers to hijack authorized client sessions by spoofing MAC-to-IP bindings. Attackers on the same network segment can send forged gratuitous ARP replies to bind their IP to a victim's MAC address, gaining unauthorized access to the portal with the victim's credentials.

Detection Guidance

Detecting this vulnerability requires monitoring for forged gratuitous ARP replies on the same Layer-2 segment. Use tools like arp-scan to check for unexpected MAC-to-IP bindings or tcpdump to capture ARP traffic for anomalies. Example commands: 'arp-scan --localnet' to list devices and 'tcpdump -i <interface> arp' to monitor ARP traffic.

Impact Analysis

This vulnerability allows attackers to impersonate authorized users on the network, potentially accessing restricted resources or services through the captive portal. It could lead to unauthorized network access, data breaches, or misuse of network privileges. Users on the same Layer-2 segment are at risk of session hijacking.

Compliance Impact

This vulnerability could lead to unauthorized access to sensitive data, violating compliance requirements for GDPR (data protection) and HIPAA (health information privacy). It may result in data breaches, unauthorized disclosures, or failure to maintain access controls, potentially leading to legal penalties or reputational damage.

Mitigation Strategies

Upgrade OPNsense to a version beyond 26.7.7 to patch the captive portal roaming vulnerability. Disable the captive portal roaming feature if not required. Implement network segmentation to restrict Layer-2 access and monitor ARP traffic for spoofing attempts.

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