External risk intelligence

Grav CMS Unsafe Deserialization and Command Injection Vulnerabilities.

CVE advisorySeverity: CRITICAL (CVSS 9.3)

CVE-2026-56700

Grav is a content management system (CMS) designed for public-facing websites. As a web application, it is commonly deployed as an internet-facing service to manage and serve content, making its underlying functions, including those affected by these vulnerabilities, reachable via standard web traffic.

OS Command Injection

Halo Surface Signal: 4 out of 5 — likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A critical vulnerability in Grav CMS could allow unauthorized attackers to execute arbitrary code on affected systems without needing any privileges. This issue arises from how the system handles certain data inputs, potentially leading to a compromise of the entire server.

Unsafe data handling can lead to full system compromise.
Affects public-facing content management systems.
Confirm relevance and exposure; remediate if applicable.

Attack Path

How an attacker could exploit the issue

An attacker could exploit these vulnerabilities by sending specially crafted input to a Grav CMS instance accessible over the internet. This input could trigger unsafe deserialization in components like the job queue, cache, or session management, or a command injection flaw during plugin/theme installation. Successfully chaining these flaws could allow an attacker to execute arbitrary code on the server.

No authentication needed to start.
Triggered by specially crafted serialized data or installation commands.
Allows arbitrary code execution on the server.

Live Threat

Current exploitation, exposure, and threat context

These vulnerabilities could allow an attacker to execute arbitrary code on the server when supported by the advisory's conditions, potentially affecting the integrity and availability of the Grav CMS and any data it manages. This could occur through specially crafted input that leverages insecure deserialization or command injection flaws, particularly when installing plugins or themes.

System code execution and data integrity.
Via insecure deserialization or command injection.
Server compromise and potential data loss.

Operational Fix

Recommended remediation, mitigation, and detection steps

The Grav CMS vulnerabilities present a critical risk, requiring immediate attention from teams responsible for web application security and infrastructure. The first practical step is to identify all Grav CMS instances, determine their exposure and criticality, and then assign ownership for remediation. The vendor-management team may also need to be involved if the affected instances are managed by a third party.

Identify Grav CMS instances and ownership.
Verify external reachability and business criticality.
Plan remediation based on risk and vendor coordination.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

Free EASM Trial See How Signal Works

Frequently asked questions

What is Grav CMS?

Grav is a flat-file content management system, meaning it stores website data in files rather than a database. It is widely used for building flexible, fast-loading websites and blogs. Because it manages site content and themes, it acts as the primary engine for rendering web pages to visitors.

What does CWE-502 mean for CVE-2026-56700?

CWE-502, or deserialization of untrusted data, occurs when software takes input and converts it into complex objects without checking if that input is malicious. In this CVE, Grav CMS processes untrusted data in its cache, session, and job queue components. Attackers can use this flaw to inject unauthorized code into the application, effectively tricking the system into running commands it was not designed to execute.

How can an attacker trigger this vulnerability?

An attacker triggers the deserialization flaws by sending specially crafted, malicious serialized data to the application, which the system processes automatically. Notably, the OS command injection issue requires admin access because it occurs during the installation of plugins or themes; simply visiting a standard page on a site does not inherently trigger the command injection vector.

Is my Grav CMS instance at risk?

According to Halo Surface Signal, Grav CMS is typically deployed as an internet-facing service to serve public content. Because these vulnerabilities allow for remote execution without requiring authentication, any instance reachable over the internet is a potential target. You should prioritize assessing any Grav instances that are publicly accessible.

What should I do to protect my system?

Your first step is to locate all Grav CMS installations in your environment and identify who manages them. Once accounted for, verify which instances are exposed to the internet. The primary remediation is to update your software to version 2.0.0-beta.2 or higher, where these issues have been addressed.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.