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

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-46431: 0.22% estimated exploitation activity in the next 30 days; percentile 12.47 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary 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. Combined with the lack of authentication (advisory #2a), no further trickery is required — any tab the developer opens has script-level read access to the stream. This advisory covers the CORS configuration in isolation. The fix is independent of authentication and bind-address fixes: the wildcard could be replaced with a same-origin echo without touching either. Details Root cause — hard-coded "" passed as the CORS allowed-origin The literal "" is the second positional argument. The vendored recwatch implementation reflects it verbatim into the response header: There is no decision based on the request's…

Published by the source

20 May 2026, 15:34 UTC

Last modified by the source

8 Jun 2026, 23:27 UTC

Source last checked

26 Oct 2026, 15:23 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-hw27-4v2q-5qff

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# Patch Next advisory brief: CVE-2026-46431

Advisory: Algernon: Auto-refresh SSE event server sets Access-Control-Allow-Origin: *
IDs: CVE-2026-46431, GHSA-hw27-4v2q-5qff
Record: https://patchnext.com/advisories/cve-2026-46431 (revision 1, source checked 26 Oct 2026, 15:23 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/xyproto/algernon 1.17.7. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/xyproto/algernon: affected <= 1.17.6; fixed in 1.17.7

## Suggested inspection (read-only)
- Go github.com/xyproto/algernon: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/xyproto/algernon.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-hw27-4v2q-5qff (GitHub-reviewed advisory GHSA-hw27-4v2q-5qff lists affected ranges: Go github.com/xyproto/algernon >=0 <=1.17.6)

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