CVE-2026-87929 in MaxSite
Summary
by MITRE • 09/09/2026
MaxSite CMS through 109.6 ships with a hardcoded session encryption key in application/config/config.php that is never changed during installation, allowing unauthenticated attackers to forge administrator session cookies. Attackers can mint a malicious ci_session cookie with administrator privileges by computing an HMAC-SHA1 using the publicly known encryption key, bypassing authentication checks in is_login() and mso_check_allow() functions.
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Analysis
by VulDB Data Team • 09/09/2026
The vulnerability identified in MaxSite CMS versions up to 109.6 represents a critical failure in cryptographic key management that fundamentally undermines the integrity of session-based authentication mechanisms. The core technical flaw resides within the application configuration file, specifically config.php, where a hardcoded secret key for encrypting and signing session data is embedded directly into the source code. This practice violates fundamental security principles regarding dynamic key generation and secure storage, as it ensures that every instance of the software deployed with this version utilizes an identical encryption credential known to any observer who can access the application's public-facing files or source repository. Because this key remains static across all installations and is never randomized during the installation process, attackers possess a universal master key capable of decrypting existing sessions or constructing new ones without requiring prior authentication credentials.
From an operational perspective, this flaw allows unauthenticated actors to forge administrator session cookies with complete impunity. By leveraging the publicly known encryption key, an attacker can compute valid HMAC-SHA1 signatures for arbitrary session data structures using standard cryptographic libraries available in most programming environments. The forged cookie is then submitted to the web server as if it were issued by a legitimate user who has successfully authenticated through the normal login process. This action effectively bypasses the security checks implemented within the is_login and mso_check_allow functions, which rely on the validity of these session tokens to determine access rights. Consequently, an attacker can elevate their privileges from anonymous visitor to full administrator without ever knowing valid usernames or passwords for existing accounts.
The impact of this vulnerability extends beyond simple unauthorized access; it enables complete compromise of the web application and potentially the underlying server infrastructure depending on how MaxSite CMS is integrated with other services. An authenticated administrator session grants the ability to modify site content, install malicious plugins, alter database configurations, and execute arbitrary code if certain administrative features are exposed or misconfigured. This scenario aligns closely with CWE-798, which classifies the use of hardcoded credentials as a severe risk factor for unauthorized access. Furthermore, the exploitation technique maps directly to MITRE ATT&CK techniques related to Credential Access and Defense Evasion, specifically involving the manipulation of session tokens to bypass authentication controls without triggering typical intrusion detection alerts associated with brute-force or credential stuffing attacks.
Mitigation strategies must prioritize immediate remediation through configuration changes rather than relying solely on software updates if a patched version is not immediately available for older deployments. The most effective solution involves replacing the hardcoded encryption key in config.php with a unique, randomly generated secret string that differs from any default value shipped with the software. This new key should be sufficiently long and complex to resist brute-force attacks while ensuring it remains confidential within the server environment. Additionally, administrators should implement strict file permission controls on configuration files containing sensitive data such as database credentials or encryption keys, restricting read access to only the web server process user where possible. Regular security audits of third-party content management systems are essential to identify similar patterns of insecure default configurations before they can be exploited in production environments.