CVE-2026-54047 Laci Synchroni Backend Vulnerable to Account Takeover / User Impersonation via Client-Side Configuration Manipulation
Attackers can impersonate any user by manipulating local config files due to missing server-side validation of OAuth2 identities against requested UIDs.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-54047?
CVE-2026-54047 is a critical authentication bypass vulnerability in LaciSynchroni server, published on 11 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Laci Synchroni is a decentralized mod and appearance sync server and plugin for Dalamud. Versions of the backend prior to 1.2.3 have an improper authentication vulnerability in the application's OAuth2 login flow. The application relies on client-side state by trusting the `UID` field inside the `Authentications` object of a user's local `config.json` file. By manually editing this local file on their PC prior to logging in, a user can supply an arbitrary UID. Because the server fails to validate that the authenticated OAuth2 identity matches the requested UID, an attacker can fully impersonate any target user and perform actions on their behalf. This issue has been resolved in version 1.2.3. The patch modifies `AuthorizeOauthAsync` inside the `SecretKeyAuthenticatorService` to strictly bind the lookup of the requested User ID (`requestedUid`) to the record of the successfully authenticated identity (`primaryUid`). The server will no longer load or return session tokens for a requested UID unless it matches the verified, authenticated database record. No known workarounds are available.
Which versions are affected by CVE-2026-54047?
How do I fix CVE-2026-54047?
No fix has been published for CVE-2026-54047 yet. Limit exposure of the affected software until one is available.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-54047 being exploited?
There is no known exploitation of CVE-2026-54047 in the wild and no public exploit code.
Sources
Also known as GHSA-gq4p-pxvg-6x9j.