CVE-2026-46430: Algernon: Auto-refresh SSE event server binds to all interfaces by default on Linux/macOS

Severity: medium (CVSS 4.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-05-26 · updated 2026-07-24
Weakness: CWE-668

Description

Algernon is a small self-contained pure-Go web server. Prior to 1.17.7, 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". This vulnerability is fixed in 1.17.7.

Affected products

xyproto algernon: before 1.17.7

References

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

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