CVE-2026-87929
CVE-2026-87929 is a critical-severity vulnerability with a CVSS 3.x base score of 9.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-321.
Key facts
- Severity: Critical (CVSS 3.x base score 9.8)
- CVSS v4: 9.3
- EPSS exploit prediction: 0% (22nd percentile)
- Actively exploited: Not listed in CISA KEV
- Weakness: CWE-321
- Published:
- Last modified:
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.
Frequently asked questions
- What is CVE-2026-87929?
- 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.
- How severe is CVE-2026-87929?
- CVE-2026-87929 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
- Is CVE-2026-87929 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (22nd percentile), an estimate of the probability of exploitation in the next 30 days.
- How do I fix CVE-2026-87929?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
- When was CVE-2026-87929 published?
- CVE-2026-87929 was published on 2026-09-09 and last updated on 2026-09-14.
References
- https://github.com/EviL0rd/maxsite-cve4/blob/main/2026.09.08-maxsite-cms-hardcoded-session-key-auth-bypass.md
- https://github.com/maxsite/cms
- https://github.com/maxsite/cms/blob/2ca0a0c7d1d71106a25dbb0f2aedaaefbf12802c/application/config/config.php#L230-L254
- https://github.com/maxsite/cms/blob/2ca0a0c7d1d71106a25dbb0f2aedaaefbf12802c/application/maxsite/common/core/init.php#L70-L96
- https://www.vulncheck.com/advisories/maxsite-cms-through-109.6-authentication-bypass-via-hardcoded-encryption-key
Other CWE-321 vulnerabilities
- CVE-2024-30207 — Critical (CVSS 10.0): A vulnerability has been identified in SIMATIC RTLS Locating Manager (6GT2780-0DA00) (All versions < V3.0.1.1), SIMATIC…
- CVE-2014-5419 — Critical (CVSS 10.0): GE Multilink ML800, ML1200, ML1600, and ML2400 switches with firmware 4.2.1 and earlier and Multilink ML810, ML3000,…
- CVE-2024-35344 — Critical (CVSS 9.9): Certain Anpviz products contain a hardcoded cryptographic key stored in the firmware of the device. This affects…
- CVE-2026-89026 — Critical (CVSS 9.8): The Issabel Framework, the web framework supporting Issabel PBX software, before commit b97dbaf contains a hard-coded…
- CVE-2026-90945 — Critical (CVSS 9.8): Crawlab through 0.6.3 uses a hard-coded HMAC-SHA256 secret for JWT token signing that cannot be overridden via…
- CVE-2026-16504 — Critical (CVSS 9.8): Deployment of the VPS.org one-click Zulip template deploys a hardcoded application signing key, a default database…