Algernon: Auto-refresh SSE event server sets Access-Control-Allow-Origin: *_CVE-2026-46431

4.3 / 10

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N

Description

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.

Basic Information

ID CVE-2026-46431

Source GitHub_M

Published May 26, 2026 at 16:42

Affected Product

Vendor xyproto

Product algernon

Version < 1.17.7

Affected Versions xyproto algernon < 1.17.7

CWE Classification

CWE-942

References

github.com /xyproto/algernon/security/advisories/GHSA-hw27-4v2q-5qff

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    "published": "2026-05-26T16:42:40.675Z",
    "modified": "2026-05-26T16:42:40.675Z",
    "type": "cve",
    "title": "Algernon: Auto-refresh SSE event server sets Access-Control-Allow-Origin: *",
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