CVE-2026-54721

silverstripe/userforms vulnerable to remote code execution via userforms email subject

Reported by

Jack Wallace from Bastion Security

The userform email subject field in the CMS is vulnerable to a specially crafted payload being used to run arbitrary code on the server.

The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths. Typical impact: varies by context: data corruption, logic bypass, or denial of service.

CVE-2026-54721 has a CVSS score of 8.8 (High). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (6.4.9, 7.0.7, 7.1.1); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

1. What is CVE-2026-54721? CVE-2026-54721 is a high-severity improper input validation vulnerability in silverstripe/userforms (composer), affecting versions < 6.4.9. It is fixed in 6.4.9, 7.0.7, 7.1.1. The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths.
2. How severe is CVE-2026-54721? CVE-2026-54721 has a CVSS score of 8.8 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of silverstripe/userforms are affected by CVE-2026-54721? silverstripe/userforms (composer) versions < 6.4.9 is affected.
4. Is there a fix for CVE-2026-54721? Yes. CVE-2026-54721 is fixed in 6.4.9, 7.0.7, 7.1.1. Upgrade to this version or later.
5. Is CVE-2026-54721 exploitable, and should I be worried? Whether CVE-2026-54721 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
6. What actually determines whether CVE-2026-54721 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.
7. How do I fix CVE-2026-54721?
   • Upgrade silverstripe/userforms to 6.4.9 or later
   • Upgrade silverstripe/userforms to 7.0.7 or later
   • Upgrade silverstripe/userforms to 7.1.1 or later

Other vulnerabilities in silverstripe/userforms