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9.2
CVE-2026-54047: Laci Synchroni server lets attackers hijack user accounts
CVE-2026-54047 · published 1 month ago
Summary
Versions of the Laci Synchroni server released before 1.2.3 trusted a user‑identifying value that could be edited in a local configuration file. By changing that file, an attacker could log in as any other user and take actions on their behalf. Update the server to version 1.2.3 or later, which validates the logged‑in identity correctly; there are no other fixes available.
What to do
The CVE record does not list a fixed version. Check the vendor's site or the advisory links below - a fix may already be released.
Affected software
| Vendor | Product | Affected versions |
|---|---|---|
| lacisynchroni | server | < 1.2.3 |
Original advisory text
Laci Synchroni Backend Vulnerable to Account Takeover / User Impersonation via Client-Side Configuration Manipulation
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.
References
- https://github.com/LaciSynchroni/server/commit/5bc3efd68b738328b8faeff089dd18a82...
- https://github.com/LaciSynchroni/server/releases/tag/v1.2.3
- https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/54xxx/CVE-2026-54047... Vendor Advisory
- https://nvd.nist.gov/vuln/detail/CVE-2026-54047 Vendor Advisory
- https://github.com/LaciSynchroni/server/security/advisories/GHSA-gq4p-pxvg-6x9j
- https://github.com/LaciSynchroni/server/pull/28
Internet-facing
14 days
Internal
At next upgrade
- Not known to be exploited
- Needs hands-on effort to exploit
- Gives an attacker full control
Type
CWE-287Improper Authentication
CWE-349Acceptance of Extraneous Untrusted Data With Trusted Data
CWE-602Client-Side Enforcement of Server-Side Security
Timeline
Published11 Sep 2026
Updated9 Oct 2026
First seen11 Sep 2026
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