External risk intelligence

MaxSite CMS Authentication Bypass Via Hardcoded Session Key

CVE advisorySeverity: CRITICAL (CVSS 9.3)

CVE-2026-87929

MaxSite CMS is a web application platform designed to host websites and content on the public internet. As a public-facing web content management system, its authentication mechanisms and session management are inherently internet-accessible in normal deployment scenarios.

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 vulnerability in MaxSite CMS involves a hardcoded session encryption key, which could allow unauthorized individuals to gain administrative access to affected systems. The issue stems from a key that is not changed during installation and is publicly known, potentially enabling attackers to bypass authentication. The primary concern is confirming if this specific technology is in use and understanding the extent of any exposure.

Website platform has a security flaw.
It allows unauthorized admin access.
Confirm relevance and assess exposure.

Attack Path

How an attacker could exploit the issue

An attacker can forge administrator session cookies by leveraging a hardcoded session encryption key found in the CMS configuration. This allows them to bypass authentication and gain administrative privileges without needing valid credentials.

No authentication required.
Forge session cookie.
Full administrative control.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability could allow unauthenticated attackers to forge administrator session cookies by leveraging a hardcoded encryption key. This bypasses authentication, potentially enabling unauthorized access to administrator functions and content management capabilities.

Administrator session cookies could be forged.
Attackers can compute HMAC-SHA1 with a known key.
Unauthorized administrator access may occur.

Operational Fix

Recommended remediation, mitigation, and detection steps

The owners of MaxSite CMS instances, likely application or web administration teams, must first confirm where this software is deployed and if it's internet-facing. Upon identification, determine the business criticality and accountable owner to prioritize remediation efforts, potentially involving vendor coordination if updates are not readily available.

Identify impacted MaxSite CMS deployments.
Verify reachability and business criticality.
Plan risk-based remediation with owners.

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 MaxSite CMS?

MaxSite CMS is a web-based content management system used to build and host websites. It provides the underlying framework and administrative interface for site owners to manage content, themes, and plugins. Because it functions as a server-side application platform, it is typically installed on web servers where it processes user requests and handles session state to keep visitors logged in.

What does CWE-321 mean for CVE-2026-87929?

CWE-321 refers to the use of a hardcoded cryptographic key. In this specific case, the software uses the same encryption key for every installation, and that key is known to the public. Because the key is fixed, the system's security relies on something that is essentially public knowledge rather than a secret unique to each deployment, failing to protect the integrity of session data.

How do attackers trigger this vulnerability?

An attacker triggers this by crafting a malicious session cookie. Because the encryption key is hardcoded and known, anyone can use it to sign a forged cookie using HMAC-SHA1. By sending this custom cookie in a web request, the attacker mimics an administrator, tricking the application into believing they are already authenticated. Normal interactions or just browsing the site without this specific forged cookie do not trigger the bypass.

Is my instance at risk according to Halo Surface Signal?

Halo Surface Signal indicates that MaxSite CMS is primarily designed to be public-facing to serve content, making its authentication mechanisms inherently reachable from the internet in standard deployments. If your instance is hosted on the public internet, it falls into the high-priority category for this vulnerability because the authentication flaw can be exploited remotely without prior access.

What should I do if I run MaxSite CMS?

Start by identifying all instances of the software within your infrastructure to determine which are internet-facing. Once you have an inventory, assess the business criticality of those specific sites. Since this issue involves a static key, consult the official vendor guidance to determine if a patch or configuration update is available to rotate or secure the session encryption process.

References

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.