CVE-2026-53724

Workarounds

Configure the storage adapter or CDN to derive Content-Type from the filename extension instead of using the stored Content-Type, or replace the default blocklist with an explicit allowlist of needed file extensions.

The default file upload extension blocklist can be bypassed by appending a trailing dot to a filename whose extension would otherwise be blocked (e.g. poc.svg.). The trailing dot causes the extension parser to extract an empty string, which short-circuits the blocklist check, and the attacker-controlled Content-Type is forwarded to the storage adapter unchanged. Storage adapters that persist and serve the provided Content-Type (such as S3 or GCS) then serve the file with an active type such as image/svg+xml, enabling stored XSS when a victim opens the file URL. The default GridFS adapter is not affected because it sets X-Content-Type-Options: nosniff on responses.

Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.

Kodem intelligence

A filename ending in a dot is now treated as extensionless. When the parser produces an empty extension, the request handler falls back to validating the Content-Type subtype against the configured extension blocklist, matching the path that already catches truly extensionless uploads with a dangerous Content-Type. This is a follow-up to the previous fix GHSA-vr5f-2r24-w5hc.

1. What is CVE-2026-53724? CVE-2026-53724 is a low-severity cross-site scripting (XSS) vulnerability in parse-server (npm), affecting versions >= 9.0.0, < 9.9.1-alpha.4. It is fixed in 9.9.1-alpha.4, 8.6.79. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
2. Which versions of parse-server are affected by CVE-2026-53724? parse-server (npm) versions >= 9.0.0, < 9.9.1-alpha.4 is affected.
3. Is there a fix for CVE-2026-53724? Yes. CVE-2026-53724 is fixed in 9.9.1-alpha.4, 8.6.79. Upgrade to this version or later.
4. Is CVE-2026-53724 exploitable, and should I be worried? Whether CVE-2026-53724 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
5. What actually determines whether CVE-2026-53724 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.
6. How do I fix CVE-2026-53724?
   • Upgrade parse-server to 9.9.1-alpha.4 or later
   • Upgrade parse-server to 8.6.79 or later

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