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.
Published: 2026-05-26
Score: 4.3 Medium
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
AI Analysis

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Remediation

No vendor fix or workaround currently provided.

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Tracking

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Advisories
Source ID Title
Github GHSA Github GHSA GHSA-hw27-4v2q-5qff Algernon: Auto-refresh SSE event server sets Access-Control-Allow-Origin: *
History

Wed, 27 May 2026 10:30:00 +0000

Type Values Removed Values Added
First Time appeared Xyproto
Xyproto algernon
Vendors & Products Xyproto
Xyproto algernon

Tue, 26 May 2026 19:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Tue, 26 May 2026 17:00:00 +0000

Type Values Removed Values Added
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.
Title Algernon: Auto-refresh SSE event server sets Access-Control-Allow-Origin: *
Weaknesses CWE-942
References
Metrics cvssV3_1

{'score': 4.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N'}


Subscriptions

Xyproto Algernon
cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-05-26T17:39:14.529Z

Reserved: 2026-05-13T22:18:22.830Z

Link: CVE-2026-46431

cve-icon Vulnrichment

Updated: 2026-05-26T17:39:03.913Z

cve-icon NVD

Status : Deferred

Published: 2026-05-26T17:16:51.100

Modified: 2026-06-17T10:53:40.107

Link: CVE-2026-46431

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-05-27T10:04:42Z

Weaknesses