# CVE-2026-46430: xyproto Algernon insecure default bind address in SSE server

Source: https://junglewise.ai/threats/cve-2026-46430-xyproto-algernon-insecure-default-bind-address-in-sse-server  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-20. Updated: 2026-05-26  
License: CC BY 4.0 with a link back

CVE-2026-46430 · Severity: medium · CVSS 4.3 · Published 2026-05-20

Algernon is a web server used by developers to build and test websites. In versions prior to 1.17.7, a background service used for live-updating pages was configured to listen on all network interfaces by default on Linux and macOS. This allows other users on the same local network (such as a public WiFi or office LAN) to see which files the developer is editing without any authorization, potentially exposing sensitive project filenames or environment variables.

Technologies: [github.com/xyproto/algernon (Go)](https://junglewise.ai/threats/technologies/github-com-xyproto-algernon), [Xyproto Algernon](https://junglewise.ai/threats/technologies/algernon). Vendors: [Go](https://junglewise.ai/threats/vendors/go), [Xyproto](https://junglewise.ai/threats/vendors/xyproto).

## Quick answers

**Is CVE-2026-46430 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-46430 being exploited in the wild.

**How severe is CVE-2026-46430?** Medium severity, with a CVSS score of 4.3, published 20 May 2026.

**Which products and versions are affected?** github.com/xyproto/algernon (Go) <= 1.17.6, SEMVER:introduced=0,fixed=1.17.7; Xyproto Algernon < 1.17.7, <= 1.17.6.

**Is there a fix for CVE-2026-46430?** Yes. github.com/xyproto/algernon (Go): upgrade to 1.17.7 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-46430 attacked?** It is attacked from the adjacent network, in a software library.

**Am I affected by CVE-2026-46430?** Check whether you run github.com/xyproto/algernon (Go) or Xyproto Algernon at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- github.com/xyproto/algernon (Go): upgrade to 1.17.7 or later

  ```sh
  go get github.com/xyproto/algernon@v1.17.7
  ```


## Technical details

Algernon web server (prior to 1.17.7) contains an insecure default initialization vulnerability where the SSE event server binds to 0.0.0.0:5553 on Linux and macOS. This occurs because the platform-dependent host default in 'engine/flags.go' was set to an empty string for non-Windows platforms, which 'utils.JoinHostPort' resolves to a wildcard bind. An attacker on the same adjacent network (LAN) can connect to the SSE endpoint without authentication to monitor file-change streams, revealing filenames and edit timings. Windows installations were unaffected as they defaulted to 'localhost'. The issue is resolved in version 1.17.7 by ensuring the SSE server defaults to the loopback interface across all platforms.

## Affected products

- xyproto Algernon < 1.17.7

## Identifiers

- CVE-2026-46430
- GHSA-gj84-924c-48fx
- GO-2026-5401

## Timeline

- 2026-05-14: advisory: GitHub Security Advisory published
- 2026-05-26: disclosed: CVE published to NVD

## References

- [https://github.com/xyproto/algernon/security/advisories/GHSA-gj84-924c-48fx](https://github.com/xyproto/algernon/security/advisories/GHSA-gj84-924c-48fx)

## Related threats

- [Algernon URL-prefix authorization bypass on case-insensitive filesystems](https://junglewise.ai/threats/cve-2026-68548-algernon-is-a-small-self-contained-pure-go-web-server-prior-to)
- [xyproto Algernon source disclosure via NTFS filename manipulation](https://junglewise.ai/threats/cve-2026-52792-xyproto-algernon-source-disclosure-via-ntfs-filename-manipulation)
- [GO-2026-5300 - Algernon: Auto-refresh SSE event server binds to all interfaces with Access-Control-Allow-Origin: * and…](https://junglewise.ai/threats/go-2026-5300-algernon-auto-refresh-sse-event-server-binds-to-all-459dcf1f)
- [xyproto Algernon path traversal and RCE via Host header](https://junglewise.ai/threats/cve-2026-48126-xyproto-algernon-path-traversal-and-rce-via-host-header)
- [xyproto Algernon permissive CORS policy in SSE event server](https://junglewise.ai/threats/cve-2026-46431-xyproto-algernon-permissive-cors-policy-in-sse-event-server)