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

> Attackers can forge administrator session cookies using a hardcoded encryption key to bypass authentication and gain full control of MaxSite CMS installations.

- **Severity:** Critical 9.3 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 9 Sep 2026
- **Updated:** 24 Sep 2026
- **Also known as:** GHSA-x43r-8q5x-82p8

## What is CVE-2026-87929?

CVE-2026-87929 is a critical vulnerability in MaxSite CMS, published on 9 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### 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.

Weakness: CWE-321 (Use of Hard-coded Cryptographic Key)

## Which versions are affected by CVE-2026-87929?


## How do I fix CVE-2026-87929?

No fix has been published for CVE-2026-87929 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-87929 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-87929 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-87929 and fix it if it is affected.

What it is: CVE-2026-87929 is a critical vulnerability in MaxSite CMS, published on 9 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-87929 exists.

Affected product: MaxSite CMS. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-87929/ (Markdown: https://insights.sbomify.com/CVE-2026-87929/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-87929
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-87929
- OSV: https://osv.dev/vulnerability/CVE-2026-87929

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-87929/
Summaries are generated and may contain mistakes; the official description above is the record.