Algernon: Auto-refresh SSE event server sets Access-Control-Allow-Origin: *
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.
- Products
- Not specified
- Affected versions
- Not specified
- Fixed versions
- Not specified
- CVEs
- CVE-2026-46431
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 2 Nov 2026, 15:33 UTC · Revision 1
Source evidence
Algernon: Auto-refresh SSE event server sets Access-Control-Allow-Origin: *
core-osv · Original sourcePublished 26 May 2026, 16:42 UTC
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.
osv:CVE-2026-46431
Complete source record
{
"id": "238053f504e58e4acb2c9006b495ea688dee0769077aa850e6d76622f87b2537",
"url": "https://osv.dev/vulnerability/CVE-2026-46431",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "Algernon: Auto-refresh SSE event server sets Access-Control-Allow-Origin: *",
"summary": "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.",
"evidence": "osv:CVE-2026-46431",
"products": [],
"severity": "medium",
"structured": {
"id": "CVE-2026-46431",
"aliases": [
"CVE-2026-46431",
"GHSA-hw27-4v2q-5qff",
"GO-2026-5440"
],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N"
}
],
"affected": [
{
"ranges": [
{
"repo": "https://github.com/xyproto/algernon",
"type": "GIT",
"events": [
{
"introduced": "0"
},
{
"fixed": "ff4de121a2aecad8cd1dbebf1e10b468e7d33ee5"
}
],
"database_specific": {
"extracted_events": [
{
"range": [
{
"introduced": "0"
},
{
"fixed": "1.17.7"
}
],
"source": "AFFECTED_FIELD",
"strategy": "StringRangeExpression"
},
{
"range": [
{
"introduced": "0"
},
{
"fixed": "1.17.7"
}
],
"source": "DESCRIPTION"
}
]
}
}
],
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],
"database_specific": {
"source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-46431.json"
}
}
],
"modified": "2026-10-28T02:30:20.567022557Z",
"provider": "osv",
"references": [
"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/46xxx/CVE-2026-46431.json",
"https://github.com/xyproto/algernon/security/advisories/GHSA-hw27-4v2q-5qff",
"https://nvd.nist.gov/vuln/detail/CVE-2026-46431"
],
"provider_metadata": {
"cwe_ids": [
"CWE-942"
],
"cna_assigner": "GitHub_M",
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/46xxx/CVE-2026-46431.json"
}
},
"related_cves": [
{
"value": "CVE-2026-46431",
"evidence": "/id"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 486585,
"published_at": "2026-05-26T16:42:40.675+00:00"
}