CVE-2026-46431
Algernon: Auto-refresh SSE event server sets Access-Control-Allow-Origin: *
CVSS Score
4.3
EPSS Score
0.0%
EPSS Percentile
0th
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.
| CWE | CWE-942 |
| Vendor | xyproto |
| Product | algernon |
| Published | May 26, 2026 |
| Last Updated | May 26, 2026 |
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CVSS v3 Breakdown
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
None
Affected Versions
xyproto / algernon
< 1.17.7