GHSA-fx3v-553x-3c4q is a low-severity (CVSS 2.8) Cross-site Scripting (XSS) vulnerability in october/backend. O3 Security confirms whether GHSA-fx3v-553x-3c4q is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Stored XSS by authenticated backend user with access to upload files
EPSS Exploitation Probability
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.
How urgent is this, really
GHSA-fx3v-553x-3c4q plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 371,256 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
october/backendReal-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
Backend users with access to upload files were permitted to upload SVG files without any sanitization applied to the uploaded files. Since SVG files support being parsed as HTML by browsers, this means that they could theoretically upload Javascript that would be executed on a path under the website's domain (i.e. /storage/app/media/evil.svg), but they would have to convince their target to visit that location directly in the target's browser as the backend does not display SVGs inline anywhere, SVGs are only displayed as image resources in the backend and are thus unable to be executed.
Patches
Issue has been patched in Build 469 (v1.0.469) & v1.1.0.
Workarounds
Apply https://github.com/octobercms/library/commit/80aab47f044a2660aa352450f55137598f362aa4 to your installation manually if unable to upgrade to Build 469 or v1.1.0.
References
Reported by Hoan Hoang
For more information
If you have any questions or comments about this advisory:
- Email us at [email protected]
Threat assessment:
<img width="1107" alt="Screen Shot 2020-10-10 at 1 47 49 PM" src="https://user-images.githubusercontent.com/7253840/95663787-378f2b80-0aff-11eb-8dfc-b97d162939da.png">Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | october/backend | ≥ 1.0.319&&< 1.0.469 | 1.0.469 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for october/backend. 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 october/backend to 1.0.469 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-fx3v-553x-3c4q 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 GHSA-fx3v-553x-3c4q 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 GHSA-fx3v-553x-3c4q. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-fx3v-553x-3c4q in your dependencies?
O3 detects GHSA-fx3v-553x-3c4q across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.