Vulnerability · Published Sep 9, 2026 · Assigned by VulnCheck

CVE-2026-87929MaxSite CMS through 109.6 Authentication Bypass via Hardcoded Encryption Key

Critical 9.8

In plain English

A critical-severity security flaw in MaxSite CMS from MaxSite. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 45% of all known vulnerabilities).

Severity (CVSS 3.1)9.8Critical

Exploit odds (30 days)0.5%top 55.2% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official description

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.

Affected products (as reported)

Vendor	Product	Versions
MaxSite	MaxSite CMS	0.78 – through 109.6

Weakness: CWE-321 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

References

https://github.com/maxsite/cms product
https://github.com/EviL0rd/maxsite-cve4/blob/main/2026.09.08-maxsite-cms-hardcoded-session-key-auth-bypass.md exploit, technical-description
https://github.com/maxsite/cms/blob/2ca0a0c7d1d71106a25dbb0f2aedaaefbf12802c/application/config/config.php#L230-L254 technical-description
https://github.com/maxsite/cms/blob/2ca0a0c7d1d71106a25dbb0f2aedaaefbf12802c/application/maxsite/common/core/init.php#L70-L96 technical-description
VulnCheck Advisory: MaxSite CMS through 109.6 Authentication Bypass via Hardcoded Encryption Key third-party-advisory