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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 Reserved 2026-05-13 | Published 2026-05-26 | Updated 2026-05-26 | Assigner GitHub_M




MEDIUM: 4.3CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N

Problem types

CWE-942: Permissive Cross-domain Policy with Untrusted Domains

Product status

< 1.17.7
affected

References

github.com/...gernon/security/advisories/GHSA-hw27-4v2q-5qff exploit

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

cve.org (CVE-2026-46431)

nvd.nist.gov (CVE-2026-46431)

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