Algernon: Auto-refresh SSE event server sets Access-Control-Allow-Origin: *

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Summary

CVECVE-2026-46431
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-05-26 17:16:51 UTC
Updated2026-05-26 19:26:42 UTC
DescriptionAlgernon 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.

Risk And Classification

Primary CVSS: v3.1 4.3 MEDIUM from [email protected]

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

EPSS: 0.000280000 probability, percentile 0.084550000 (date 2026-05-27)

Problem Types: CWE-942 | CWE-942 CWE-942: Permissive Cross-domain Policy with Untrusted Domains

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary4.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N
3.1CNADECLARED4.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
None

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Xyproto Algernon affected < 1.17.7 Not specified

References

ReferenceSourceLinkTags
github.com/xyproto/algernon/security/advisories/GHSA-hw27-4v2q-5qff 134c704f-9b21-4f2e-91b3-4a467353bcc0 github.com
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