CVE-2026-46431CWE-942

Algernon: Auto-refresh SSE event server sets Access-Control-Allow-Origin: *

Medium · published May 26, 2026

CVSS v3.1
4.3
EPSS
0%
Percentile
22.2
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v3.1
4.3 · MEDIUM
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N
CVSS v4.0
Not supplied
EPSS
0.00306 · 22.2th percentile
Weakness
CWE-942 · Permissive Cross-domain Security Policy with Untrusted Domains
Published
2026-05-26T16:42Z
EPSS history
Timeline
  • 26 MAY 16:42Z
    Algernon: Auto-refresh SSE event server sets Access-Control-Allow-Origin: *
    cvelistv5