CVE-2026-54721 is a high-severity (CVSS 8.8) Code Injection vulnerability in silverstripe/userforms. O3 Security confirms whether CVE-2026-54721 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
silverstripe/userforms vulnerable to remote code execution via userforms email subject
Real-World Exposure
silverstripe/userforms🐘silverstripe/userforms🐘silverstripe/userformsReal-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
Impact
The userform email subject field in the CMS is vulnerable to a specially crafted payload being used to run arbitrary code on the server.
Reported by
Jack Wallace from Bastion Security
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | silverstripe/userforms | all versions | 6.4.9 |
| 🐘Packagist | silverstripe/userforms | ≥ 7.0.0&&< 7.0.7 | 7.0.7 |
| 🐘Packagist | silverstripe/userforms | ≥ 7.1.0&&< 7.1.1 | 7.1.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for silverstripe/userforms. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update silverstripe/userforms to 6.4.9 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-54721 is resolved across your whole dependency graph.
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.
How O3 protects you
O3 pinpoints whether CVE-2026-54721 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-54721. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-54721 in your dependencies?
O3 detects CVE-2026-54721 across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.