CVE-2026-87929: Use of Hard-coded Cryptographic Key in MaxSite MaxSite CMS
Affects MaxSite MaxSite CMSSource CVE Database V5
Not known to be exploited · CVSS 9.3 Critical.
Data as of 10/25/2026, 04:40:14 UTC
- Exploitation
Not in CISA KEV, no exploitation reported
- EPSS
- 0.5% chance of exploitation in 30 days – higher than 43% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:NWhat to do
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| MaxSiteMaxSite CMS | Affected
| Fixed in– |
GitHubMaxSite CMSpkg:github/MaxSite CMSOther threats | Affected
| Fixed in– |
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
AI-suggested
Until a fix is available, users should consider restricting access to the CMS or implementing additional authentication controls to mitigate risk.
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.
Impact
The vulnerability enables unauthenticated attackers to gain administrator-level access to the MaxSite CMS by forging session cookies. This compromises the integrity and confidentiality of the CMS, potentially allowing full control over the affected system without any authentication.
References
- github.com/maxsite/cms (opens in a new tab)
- github.com/EviL0rd/maxsite-cve4/blob/main/2026.09.08-maxsite-cms-hardcoded-session-key-auth-bypass.md (opens in a new tab)
- github.com/maxsite/cms/blob/2ca0a0c7d1d71106a25dbb0f2aedaaefbf12802c/application/config/config.php (opens in a new tab)
- github.com/maxsite/cms/blob/2ca0a0c7d1d71106a25dbb0f2aedaaefbf12802c/application/maxsite/common/core/init.php (opens in a new tab)
- vulncheck.com/advisories/maxsite-cms-through-109.6-authentication-bypass-via-hardcoded-encryption-key (opens in a new tab)