CVE-2026-54721: Silverstripe userforms remote code execution in email subject

CVE-2026-54721 · Severity: high · CVSS 8.8 · Published 2026-08-27

Silverstripe userforms is a widely-used CMS extension that allows administrators to create and manage user forms with email notifications. The email subject field lacks proper input validation, allowing authenticated CMS users to inject and execute arbitrary server-side code. An attacker with limited CMS access can fully compromise the server, steal sensitive data, or disrupt service availability.

Technologies: silverstripe/userforms (Packagist). Vendors: Packagist, Silverstripe.

Quick answers

Is CVE-2026-54721 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-54721 being exploited in the wild.
How severe is CVE-2026-54721?
High severity, with a CVSS score of 8.8, published 27 August 2026.
Which products and versions are affected?
silverstripe/userforms (Packagist) ECOSYSTEM:introduced=0,fixed=6.4.9; Silverstripe UserForms < 6.4.9.
Is there a fix for CVE-2026-54721?
Yes. silverstripe/userforms (Packagist): upgrade to 6.4.9 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-54721 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-54721?
Check whether you run silverstripe/userforms (Packagist) or Silverstripe UserForms at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • silverstripe/userforms (Packagist): upgrade to 6.4.9 or later
    composer require silverstripe/userforms:^6.4.9

Technical details

This vulnerability is a code injection flaw (CWE-94) resulting from improper input validation (CWE-20) in the userform email subject field. The vulnerable component accepts user-supplied input through the CMS interface without proper sanitization before it is used in dynamic code generation or execution. The attack requires network access and low-privilege CMS authentication; no user interaction is required. An authenticated attacker can craft a payload that executes with the privileges of the web application process, achieving complete confidentiality, integrity, and availability compromise. Patches are available in versions 6.4.9, 7.0.7, and 7.1.1, addressing the vulnerability by implementing proper input validation and neutralizing special elements in email subject handling.

Affected products

  • Silverstripe userforms < 6.4.9
  • Silverstripe userforms >= 7.0.0, < 7.0.7
  • Silverstripe userforms >= 7.1.0, < 7.1.1

Identifiers

  • CVE-2026-54721
  • GHSA-g8wr-r2v2-vqc6

Timeline

  • 2026-06-24: disclosed: Vulnerability published to GitHub Advisory Database
  • 2026-06-24: patched: Patches released: version 6.4.9, 7.0.7, 7.1.1
  • 2026-08-27: advisory: Advisory updated and reviewed on GitHub

References

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