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CVE-2026-28781 — craftcms/cms

Fix: craftcms/cms@830b403

CVE-2026-28781 is a CWE-639 vulnerability in craftcms/cms. A fix is available for craftcms/cms — see the affected versions and patch details below.

Craft Affected by Entries Authorship Spoofing via Mass Assignment

Also known asGHSA-2xfc-g69j-x2mp
Published
Mar 4, 2026
Updated
Aug 12, 2026
Affected
2 pkgs
Patched
2 / 2
Exploits
None indexed
Exploitation data as of Sep 24, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

Proof-of-concept exploit code exists

  • CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-28781.

EPSS Exploitation Probability

via FIRST.org ↗
0.4%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs34th percentile — riskier than 34% of all scored CVEsHighest risk

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Real-World Exposure

2 pkgs affected
🐘craftcms/cms🐘craftcms/cms

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.

Description

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., 1 for the default Admin).

Steps to Reproduce

  1. Log in as the attacker
  2. Navigate to the "Entries" section and click "New Entry"
  3. Fill in the required fields
  4. Enable a proxy tool (e.g., Burp Suite) to intercept requests
  5. Click "Save" & Intercept the request
  6. In the request body, add a new parameter to the body params: &authorIds[]=<Victim_ID>
  7. Forward the request
  8. Log in as an admin / as with the victim account
  9. Go to entries & Observe the newly created entry is listed and the author is the victim account, not the actual creator

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.

Resources

https://github.com/craftcms/cms/commit/c6dcbdffaf6ab3ffe77d317336684d83699f4542 https://github.com/craftcms/cms/commit/830b403870cd784b47ae42a3f5a16e7ac2d7f5a8

Affected Packages

2 total 2 fixed
EcosystemPackageVulnerable rangeFix
🐘Packagistcraftcms/cms≥ 5.0.0-RC1&&< 5.9.0-beta.15.9.0-beta.1composer require craftcms/cms:^5.9.0-beta.1
🐘Packagistcraftcms/cms≥ 4.0.0-RC1&&< 4.17.0-beta.14.17.0-beta.1composer require craftcms/cms:^4.17.0-beta.1

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for craftcms/cms, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update craftcms/cms to 5.9.0-beta.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-28781 is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

  4. How O3 protects you

    O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-28781 can be triaged on real exposure rather than presence alone.

Tailored to CVE-2026-28781. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

## 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 ##
O3 Security · Impact-Aware SCA

Is CVE-2026-28781 in your dependencies?

O3 Security finds CVE-2026-28781 across Packagist dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.

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CVE-2026-28781: craftcms/cms | O3 Security