Summary
Craft CMS has Twig Function Blocklist Bypass
Craft CMS implements a blocklist to prevent potentially dangerous PHP functions from being called via Twig non-Closure arrow functions.
In order to be able to successfully execute this attack, you need to either have allowAdminChanges enabled on production, or a compromised admin account, or an account with access to the System Messages utility.
Several PHP functions are not included in the blocklist, which could allow malicious actors with the required permissions to execute various types of payloads, including RCEs, arbitrary file reads, SSRFs, and SSTIs.
Twig has already deprecated this behavior, and it will eventually be removed from Twig altogether.
This has been resolved in Craft 4.17.0 and 5.9.0, which removes the blocklist and disables all non-Clousure arrow functions in Twig globally via the enableTwigSandbox config setting. That setting is enabled by default on all new Craft projects. Existing Craft projects will need to enable the config setting to take advantage of it.
Existing projects should update to the patched versions of 5.9.0 and 4.17.0 to mitigate the issue and enable the config setting.
Resources
Impact
Untrusted input is evaluated as executable code within the application's runtime environment. Typical impact: arbitrary code execution within the application's privilege context.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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craftcms/cms to 5.9.0-beta.1 or later; craftcms/cms to 4.17.0-beta.1 or later
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2026-28783? CVE-2026-28783 is a medium-severity code injection vulnerability in craftcms/cms (composer), affecting versions >= 5.0.0-RC1, < 5.9.0-beta.1. It is fixed in 5.9.0-beta.1, 4.17.0-beta.1. Untrusted input is evaluated as executable code within the application's runtime environment.
- Which versions of craftcms/cms are affected by CVE-2026-28783? craftcms/cms (composer) versions >= 5.0.0-RC1, < 5.9.0-beta.1 is affected.
- Is there a fix for CVE-2026-28783? Yes. CVE-2026-28783 is fixed in 5.9.0-beta.1, 4.17.0-beta.1. Upgrade to this version or later.
- Is CVE-2026-28783 exploitable, and should I be worried? Whether CVE-2026-28783 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-28783 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-28783?
- Upgrade
craftcms/cmsto 5.9.0-beta.1 or later - Upgrade
craftcms/cmsto 4.17.0-beta.1 or later
- Upgrade