# CVE-2026-70554: MaxSite CMS Unauthenticated PHP Object Injection via maxsite_comuser Cookie

> Unauthenticated attackers can achieve remote code execution in MaxSite CMS by sending malicious serialized data in the maxsite_comuser cookie.

- **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:** 4 Aug 2026
- **Updated:** 24 Sep 2026
- **Also known as:** GHSA-jm66-348j-qvv2

## What is CVE-2026-70554?

CVE-2026-70554 is a critical unsafe deserialization vulnerability in MaxSite CMS, published on 4 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

MaxSite CMS contains a PHP object injection vulnerability that allows unauthenticated attackers to execute arbitrary code by passing attacker-controlled serialized data in the maxsite_comuser cookie directly to unserialize() without validation or class allowlisting. Attackers can craft a malicious serialized PHP object payload delivered in a single HTTP request to trigger magic methods during object graph reconstruction, enabling property-oriented programming attacks or remote code execution via available gadget chains such as those targeting SoapClient or Imagick extensions.

Weakness: CWE-502 (Deserialization of Untrusted Data)

## Which versions are affected by CVE-2026-70554?


## How do I fix CVE-2026-70554?

No fix has been published for CVE-2026-70554 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-70554 being exploited?

There is no known exploitation of CVE-2026-70554 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-70554 and fix it if it is affected.

What it is: CVE-2026-70554 is a critical unsafe deserialization vulnerability in MaxSite CMS, published on 4 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-70554 in the wild and no public exploit code.

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-2026-70554/ (Markdown: https://insights.sbomify.com/CVE-2026-70554/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-70554
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-70554
- OSV: https://osv.dev/vulnerability/CVE-2026-70554

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-70554/
Summaries are generated and may contain mistakes; the official description above is the record.