CVE-2026-46431
Algernon: Auto-refresh SSE event server sets Access-Control-Allow-Origin: *
MEDIUM 4.3EPSS 0.3%
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.
- Affected
- xyproto · algernon
- CVSS v3.1 GITHUB
- 4.3 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N - EPSS
- 0.31% chance of exploitation in the next 30 days, 22nd percentile
- Published
- 2026-05-26