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CVE-2026-70553 – Unauthenticated Remote Code Execution – MaxSite CMS 105.2 through 109.5

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Summary

CVE-2026-70553 is a critical unauthenticated remote code execution vulnerability in MaxSite CMS. An attacker can inject arbitrary PHP code into the application configuration file by sending crafted POST requests to the install endpoint after installation is complete, resulting in full compromise of the affected server. The issue is rated critical (CVSS v4.0 9.3).

Technical details

  • Root cause: Improper control of code generation (CWE-94) in the install endpoint, which fails to properly validate attacker-supplied input that is written into the application configuration file.
  • Trigger conditions: The install endpoint remains reachable and exploitable even after installation has been completed; no authentication and no user interaction are required.
  • Attack vector: Network — remote, unauthenticated HTTP POST requests to the install endpoint.
  • Impact: Injection of arbitrary PHP code into the configuration file leads to remote code execution in the context of the web server, enabling full system compromise, data theft, and service disruption.

Affected software

  • MaxSite CMS versions 105.2 through 109.5 (inclusive).
  • Fixed in MaxSite CMS 109.6 and later.

Severity

  • CVSS v3.1 base score: 9.8 (Critical) — CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  • CVSS v4.0 base score: 9.3 (Critical) — 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

Mitigation and recommended actions

  • Immediate: Upgrade to MaxSite CMS 109.6 or later, which remediates the vulnerability.
  • If no patch can be applied: Restrict or remove access to the install endpoint, block it at the web server or a reverse proxy/WAF, and limit network exposure of the application to trusted sources until the upgrade is applied.

How IONIX identifies potentially affected assets

IONIX matches the following signals against data already collected when it crawled the asset; identifying the technology sends no request beyond that crawl.

  • generator meta tag content: MaxSite CMS

References

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Map your entire attack surface (continously)

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Dozens of threat intel feeds using agentic technology are continuously analyzed to detect the appearance of proof-of-concept code, exploit kits, and indicators of active targeting. IONIX goes further by applying AI to proactively evaluate whether emerging vulnerabilities are likely to be exploited, even before PoCs go public.

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Identify Potential External Exposures

Not all CVEs matter. IONIX filters vulnerabilities by asking attacker-centric questions: Can it be reached from the internet? Does it require authentication? Is it being exploited in the wild? This dramatically reduces noise and focuses teams on threats that can actually be weaponized.

4

Create Safe, Scalable Exploit Validations

IONIX transforms real-world PoCs into safe, non-intrusive test payloads that can be run in production environments without disruption. These simulations are precisely targeted to the systems that are vulnerable, ensuring rapid validation without unnecessary load.

5

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By combining context about software stack, versioning, exposure status, and reachability, IONIX ensures that only the right payloads are executed against the right assets, maximizing efficiency and minimizing risk.

6

Drive Fast and Actionable Remediation

Results are routed through integrations with ticketing, SOAR, and SIEM tools. Issues are written in plain language, bundled into remediation clusters, and prioritized based on asset criticality, exploitability, and blast radius. This shortens mean time to remediation (MTTR) and empowers teams to act with confidence.

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