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Vulnerability record · CVE-2026-54047 · published 11 September 2026

CVE-2026-54047: Improper authentication vulnerability

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.

9.2 CVSS 4.0 Critical EPSS 0.30% · top 79.3% CWE-287 · Improper authenticationCWE-349 · CWE-349 Received
9.2CVSS 4.0 base score
0.30%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
4References
11 Sep 2026Last modified by NVD

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.

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

References

LinkTags
https://github.com/LaciSynchroni/server/commit/5bc3efd68b738328b8faeff089dd18a826ec9ca4
https://github.com/LaciSynchroni/server/pull/28
https://github.com/LaciSynchroni/server/releases/tag/v1.2.3
https://github.com/LaciSynchroni/server/security/advisories/GHSA-gq4p-pxvg-6x9j

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Source: NIST National Vulnerability Database (record CVE-2026-54047), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.