CVE-2026-46431 — Algernon: Auto-refresh SSE event server sets Access-Control-Allow-Origin: *
Algernon is a small self-contained pure-Go web server. Prior to 1.17.7, the SSE event server's Access-Control-Allow-Origin response header was hardcoded to the wildcard * regard…
Published: 2026-05-26 · CVSS: 4.3 · CVSS 3.1
Algernon is a small self-contained pure-Go web server. Prior to 1.17.7, the SSE event server's Access-Control-Allow-Origin response header was hardcoded to the wildcard * regardless of the caller's Origin. Because EventSource does not preflight and does not send cookies, the wildcard is sufficient to let any third-party page the developer visits open a cross-origin EventSource to the SSE port and read the live filename stream from JavaScript. This vulnerability is fixed in 1.17.7.
Source: CVE Program · Revision 8b16575c39f1e1810c5e863010da073d2d3285e7