Critical severity · published Sep 9, 2026
CVE-2026-87929
MaxSite CMS through 109.6 Authentication Bypass via Hardcoded Encryption Key
9.8
CVSS
0.5%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
High
Integrity
High
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.5% · higher than 45% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MC
MaxSite CMS · MaxSite
0.78 through 109.6 · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-87929
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-87929
github.com
https://github.com/EviL0rd/maxsite-cve4/blob/main/2026.09.08-maxsite-cms-hardcoded-session-key-auth-bypass.md
github.com
https://github.com/maxsite/cms
github.com
https://github.com/maxsite/cms/blob/2ca0a0c7d1d71106a25dbb0f2aedaaefbf12802c/application/config/config.php#L230-L254
github.com
https://github.com/maxsite/cms/blob/2ca0a0c7d1d71106a25dbb0f2aedaaefbf12802c/application/maxsite/common/core/init.php#L70-L96
www.vulncheck.com
https://www.vulncheck.com/advisories/maxsite-cms-through-109.6-authentication-bypass-via-hardcoded-encryption-key
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