CVE-2026-49819: SERIOUSM4X Upsnap

Critical severity, CVSS 9.8. EPSS: 1.1% chance of exploitation in the next 30 days.

UpSnap is a wake on lan web app. Versions 4.4.1 through 5.3.5 are vulnerable to a missing-authentication / privilege-escalation chain in `pb.HandlerInitSuperuser` (`backend/pb/handlers.go:249`), reachable as `POST /api/upsnap/init-superuser`. The vulnerable code lacks any authentication, setup token, IP allow-list, or rate limit and is gated only by a `totalSuperusers > 0` count check — a condition that is false on every fresh install — allowing an unauthenticated network-adjacent attacker to register the initial superuser account, receive a long-lived JWT, and pivot to root remote code execution at `backend/networking/wake.go:43` (`exec.CommandContext(ctx, "/bin/sh", "-c", wake_cmd)`). Version 5.4.0 fixes the issue.

Affected products

• SERIOUSM4X Upsnap: from 4.4.1, before 5.4.0 (fixed in 5.4.0)

Published 2026-08-13. Last modified 2026-09-09.