# CVE-2026-87929

## Summary

- **CVE ID:** CVE-2026-87929
- **Severity:** CRITICAL
- **CVSS Score:** 9.8 (CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N)
- **CWE:** CWE-321
- **Published:** Sep 9, 2026
- **Last Modified:** Sep 9, 2026

## 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

- MaxSite — MaxSite CMS (0.78)

## References

- [CNA](https://github.com/maxsite/cms)
- [CNA](https://github.com/EviL0rd/maxsite-cve4/blob/main/2026.09.08-maxsite-cms-hardcoded-session-key-auth-bypass.md)
- [CNA](https://github.com/maxsite/cms/blob/2ca0a0c7d1d71106a25dbb0f2aedaaefbf12802c/application/config/config.php#L230-L254)
- [CNA](https://github.com/maxsite/cms/blob/2ca0a0c7d1d71106a25dbb0f2aedaaefbf12802c/application/maxsite/common/core/init.php#L70-L96)
- [CNA](https://www.vulncheck.com/advisories/maxsite-cms-through-109.6-authentication-bypass-via-hardcoded-encryption-key)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.29%
- **EPSS Percentile:** 21.1

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-11._