Algernon: Auto-refresh SSE event server binds to all interfaces by default on Linux/macOS

Exploitation

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

CVSS

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

EPSS

• CVE-2026-46430: 0.20% estimated exploitation activity in the next 30 days; percentile 9.49 (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 bound to 0.0.0.0:5553 on Linux/macOS by default because the platform-dependent host default in engine/flags.go:39-46 set host = "" for non-Windows, and utils.JoinHostPort("", ":5553") resolves to ":5553" — a Go http.Server.Addr of ":5553" listens on every interface. On Windows the same code chose "localhost", binding loopback only. The result was a platform split where the OS Algernon's dev workflow is most often used on (Linux/macOS) got the network-exposed default, and only Windows users got the loopback-safe one. A LAN peer with no developer interaction could connect to <dev-laptop-ip:5553 and read the file-change stream. This advisory covers the bind-address default in isolation. The fix is independent of authentication (#2a) and CORS (#2b) — switching the default to loopback can be done without touching either. Details Root cause — platform-dependent host default in handleFlags Result tabulated: | Platform | host | eventAddr after JoinHostPort |…

Published by the source

20 May 2026, 15:33 UTC

Last modified by the source

20 May 2026, 15:33 UTC

Source last checked

26 Oct 2026, 15:22 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-gj84-924c-48fx

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# Patch Next advisory brief: CVE-2026-46430

Advisory: Algernon: Auto-refresh SSE event server binds to all interfaces by default on Linux/macOS
IDs: CVE-2026-46430, GHSA-gj84-924c-48fx
Record: https://patchnext.com/advisories/cve-2026-46430 (revision 1, source checked 26 Oct 2026, 15:22 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-gj84-924c-48fx (GitHub-reviewed advisory GHSA-gj84-924c-48fx lists affected ranges: Go github.com/xyproto/algernon >=0 <=1.17.6)

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