CVE-2026-46431

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.

Affected Software

Weaknesses

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

ADP Enrichment

CISA ADP Vulnrichment

• SSVC:
• Exploitation: poc
  • Automatable: no
  • Technical Impact: partial

Additional References

• https://github.com/xyproto/algernon/security/advisories/GHSA-hw27-4v2q-5qff

References

• https://github.com/xyproto/algernon/security/advisories/GHSA-hw27-4v2q-5qff

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