PatchSiren cyber security CVE debrief

CVE-2026-50873 flatnotes CVE debrief

CVE-2026-50873 is an arbitrary file upload vulnerability in the attachment handling component of flatnotes v5.5.4. This vulnerability allows attackers to execute arbitrary code by uploading a crafted HTML or SVG file.

Vendor: flatnotes
Product: flatnotes
CVSS: Unknown
CISA KEV: Not listed in stored evidence
Original CVE published: 2026-06-15
Original CVE updated: 2026-06-15
Advisory published: 2026-06-15
Advisory updated: 2026-06-15

Who should care

Users of flatnotes v5.5.4 should be aware of this vulnerability and take steps to mitigate it.

Technical summary

The vulnerability is caused by inadequate validation of uploaded files, allowing attackers to upload malicious files that can be executed on the server.

Defensive priority

High

Recommended defensive actions

Update flatnotes to a version that fixes this vulnerability, if available.
Restrict file uploads to only allow specific, validated file types.
Monitor server logs for suspicious activity related to file uploads.

Evidence notes

Evidence for this CVE comes from [ref-4](https://gist.github.com/pyuysig/ab0af5b10877fb906941e05a69b202a7).

Official resources

CVE-2026-50873 was published on 2026-06-15T20:16:30.097Z and has not been modified since.