CVE-2026-76731: HPE Networking Instant On Auth Bypass Flaw

CVE-2026-76731 Overview

CVE-2026-76731 is an authentication bypass vulnerability in the captive portal component of HPE Networking Instant On. An unauthenticated remote attacker can circumvent existing authentication controls over the network without user interaction. Successful exploitation grants limited access to data and permits limited modifications within the affected component.

The vulnerability is exploitable over the network with low attack complexity and requires no privileges. HPE has published a security bulletin documenting the issue and providing remediation guidance for affected deployments.

Critical Impact
Remote unauthenticated attackers can bypass captive portal authentication, gaining limited read and write access to the affected component without any user interaction.

Affected Products

HPE Networking Instant On (captive portal component)
Refer to the HPE security bulletin for specific affected firmware versions
Deployments exposing the captive portal to untrusted networks are at greatest risk

Discovery Timeline

2026-09-29 - CVE-2026-76731 published to NVD
2026-09-29 - Last updated in NVD database

Technical Details for CVE-2026-76731

Vulnerability Analysis

The vulnerability resides in the captive portal of HPE Networking Instant On devices. Captive portals typically intercept client HTTP traffic and require authentication before granting network access. A defect in the authentication enforcement logic allows an attacker to reach protected functionality without presenting valid credentials.

The impact is scoped to limited confidentiality and integrity effects on the captive portal component itself. Availability is not affected. Because the attack vector is network-based and requires no privileges or user interaction, exposed portals can be targeted directly by remote clients.

Root Cause

HPE has not published detailed root-cause information in the referenced bulletin. The described behavior is consistent with an authentication bypass class weakness, where the component fails to properly validate or enforce authentication state before servicing requests to protected resources.

Attack Vector

An attacker interacts with the captive portal over the network, sending crafted requests that bypass authentication checks. No credentials, tokens, or user interaction are required. Once bypassed, the attacker can read a limited subset of data exposed by the portal and perform a limited set of state-changing operations.

No public exploit code, proof-of-concept, or CISA KEV listing is currently associated with CVE-2026-76731. See the HPE Security Bulletin for vendor-provided technical details.

Detection Methods for CVE-2026-76731

Indicators of Compromise

Unexpected successful requests to captive portal administrative or protected endpoints without preceding authentication events
Configuration or session changes on the captive portal that do not correlate with authenticated administrator activity
Anomalous client sessions originating from untrusted network segments interacting with portal APIs

Detection Strategies

Inspect HTTP/HTTPS logs from Instant On devices for requests to protected portal paths that lack corresponding authentication events
Alert on portal responses returning protected content to sessions that never completed the login workflow
Correlate portal activity with network flow data to identify sources bypassing the standard authentication path

Monitoring Recommendations

Forward captive portal and management-plane logs to a centralized logging or SIEM platform for retention and correlation
Baseline normal captive portal request patterns and alert on deviations in request paths, methods, or response codes
Monitor administrative changes to captive portal configuration and enforce change-management review

How to Mitigate CVE-2026-76731

Immediate Actions Required

Review the HPE Security Bulletin and identify affected Instant On devices in your environment
Apply the vendor-supplied firmware update as soon as it is available for your deployment
Restrict network reachability to the captive portal management and authentication interfaces from untrusted networks

Patch Information

HPE has published guidance in bulletin hpesbnw05150en_us. Administrators should consult the bulletin for the specific fixed firmware versions applicable to their HPE Networking Instant On hardware and deploy the updates through the standard Instant On management workflow.

Workarounds

Segment captive portal traffic onto isolated VLANs and limit exposure to only required client networks
Place upstream access controls or a web application firewall in front of the portal to filter unauthenticated requests to protected endpoints
Disable the captive portal feature on devices where it is not required until patches are applied

bash

# Configuration example
# Restrict inbound access to captive portal management interfaces
# Replace <portal_ip> and <trusted_subnet> with your values
iptables -A INPUT -p tcp --dport 443 -s <trusted_subnet> -d <portal_ip> -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -d <portal_ip> -j DROP