CVE-2026-46431: 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…

PriorityP422medium4.3CVSS 3.1

AVNACLPRNUIRSUCLINAN

EPSS

0.22%

12.3th percentile

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

2 ranges

Vendor	Product	Version range	Fixed in
github.com	xyproto_algernon	>= 0 < 1.17.7	1.17.7
xyproto	algernon	< 1.17.7	1.17.7

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