Summary
Craft CMS: Entries Authorship Spoofing via Mass Assignment
Description
The entry creation process allows for Mass Assignment of the authorId attribute. A user with "Create Entries" permission can inject the authorIds[] (or authorId) parameter into the POST request, which the backend processes without verifying if the current user is authorized to assign authorship to others.
Normally, this field is not present in the request for users without the necessary permissions. By manually adding this parameter, an attacker can attribute the new entry to any user, including Admins. This effectively "spoofs" the authorship.
Proof of Concept
Prerequisites
- A user account with "Create Entries" permission for a section.
- Victim's account ID (e.g.,
1for the default Admin).
Steps to Reproduce
- Log in as the attacker
- Navigate to the "Entries" section and click "New Entry"
- Fill in the required fields
- Enable a proxy tool (e.g., Burp Suite) to intercept requests
- Click "Save" & Intercept the request
- In the request body, add a new parameter to the body params:
&authorIds[]=<Victim_ID> - Forward the request
- Log in as an admin / as with the victim account
- Go to entries & Observe the newly created entry is listed and the author is the victim account, not the actual creator
Resources
https://github.com/craftcms/cms/commit/c6dcbdffaf6ab3ffe77d317336684d83699f4542
https://github.com/craftcms/cms/commit/830b403870cd784b47ae42a3f5a16e7ac2d7f5a8
Impact
- A user can create entries that appear to belong to higher-privileged users, potentially bypassing review processes or gaining trust based on false authorship.
- An attacker could post malicious or inappropriate content attributed to an administrator or other trusted users.
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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See it in your environmentNew to Kodem? Get a demo →Remediation advice
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-2026-28781? CVE-2026-28781 is a medium-severity security 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.
- Which versions of craftcms/cms are affected by CVE-2026-28781? craftcms/cms (composer) versions >= 5.0.0-RC1, < 5.9.0-beta.1 is affected.
- Is there a fix for CVE-2026-28781? Yes. CVE-2026-28781 is fixed in 5.9.0-beta.1, 4.17.0-beta.1. Upgrade to this version or later.
- Is CVE-2026-28781 exploitable, and should I be worried? Whether CVE-2026-28781 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-2026-28781 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-2026-28781?
- Upgrade
craftcms/cmsto 5.9.0-beta.1 or later - Upgrade
craftcms/cmsto 4.17.0-beta.1 or later
- Upgrade