External risk intelligence

Headless Single Sign On Unauthenticated Bypass Vulnerability

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2026-28148

The vulnerability affects a Single Sign-On (SSO) solution. SSO systems and identity portals are designed to be public-facing by nature to facilitate authentication for users and services, making them inherently reachable from the internet in standard deployments.

Halo Surface Signal: 5 out of 5 — more likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

This advisory concerns a critical vulnerability in Headless Single Sign On technology that allows unauthenticated access to bypass security controls. The issue is significant because Single Sign-On systems are central to user authentication and access management. Unmitigated, this could potentially expose sensitive systems and data.

Bypass controls without any login.
Affects core authentication systems.
Confirm relevance and exposure.

Attack Path

How an attacker could exploit the issue

An attacker could exploit this vulnerability by sending specially crafted requests over the network, bypassing authentication mechanisms. This could allow them to gain unauthorized access and potentially perform actions with elevated privileges. The vulnerability lies in the Single Sign-On component, which is often exposed publicly to facilitate user access.

Unauthenticated network access required.
Bypass authentication in the Single Sign-On.
Unauthorized access and control.

Live Threat

Current exploitation, exposure, and threat context

A critical vulnerability exists in Headless Single Sign On that could allow unauthenticated attackers to bypass security controls. This bypass, when successful, could lead to unauthorized access to sensitive information or the ability to alter system configurations. The impact is amplified because such systems often manage user authentication and access to multiple services.

System authentication controls.
Unauthenticated network access.
Unauthorized access to data.

Operational Fix

Recommended remediation, mitigation, and detection steps

This unauthenticated bypass vulnerability in Headless Single Sign-On impacts systems where this authentication mechanism is exposed externally. The first step for technical leaders and security teams is to identify all instances of this technology, confirm their reachability and business criticality, and then locate the accountable owner for remediation planning.

Application owners and platform teams should own the issue.
Verify external reachability and business criticality first.
Plan remediation based on identified risk exposure.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is Headless Single Sign On and how is it used?

Headless Single Sign On is a software component designed to manage identity and user authentication across multiple services without requiring a traditional front-end interface. It acts as a central gatekeeper, allowing applications to verify user credentials and manage session tokens automatically. Developers integrate it into their ecosystems to streamline secure access, ensuring that various services can trust a user's identity once they have been verified through this central system.

What does CWE-347 mean in the context of CVE-2026-28148?

CWE-347 refers to Improper Verification of Cryptographic Signature. In this vulnerability, the system fails to correctly validate the digital signatures or security tokens presented during the login process. Because the software does not properly confirm that these tokens are authentic, an attacker can provide forged or invalid credentials that the system mistakenly accepts as legitimate, allowing them to bypass mandatory login barriers entirely.

How does an attacker trigger this bypass vulnerability?

An attacker triggers this flaw by sending specifically crafted network requests to the affected Single Sign-On service. The vulnerability relies on the system's failure to enforce authentication for these incoming requests. It is important to note that this bug does not require any interaction from legitimate users or existing valid accounts; the attacker simply needs the ability to communicate with the service over the network to successfully circumvent security controls.

Is my system at risk if it uses this software?

Halo Surface Signal indicates that your risk level is high because Single Sign-On solutions are fundamentally designed to be internet-facing to support distributed users and services. Since the software is typically reachable from the public internet, it lacks the protection of being hidden behind a private network. If your instance is accessible externally, it is a primary candidate for this type of unauthenticated access attempt.

What should I do first to manage this security risk?

Begin by auditing your infrastructure to locate every instance of the Headless Single Sign On plugin currently in use. Once you have identified these systems, assess whether they are reachable from the public internet or restricted to internal traffic. After mapping their exposure and importance to your business, coordinate with the system owners to prioritize and plan your remediation steps to close this security gap.

References

patchstack.com/database/wordpress/plugin/headless-single-sign-on/vul…

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.