CVE-2026-54047: CWE-287: Improper Authentication in LaciSynchroni server
Laci Synchroni server versions prior to 1.2.3 contain an improper authentication vulnerability in the OAuth2 login flow. The server trusts a client-side UID value from a local config file without verifying it against the authenticated identity, allowing attackers to impersonate any user. This critical vulnerability has been fixed in version 1.2.3 by enforcing strict binding between the requested UID and the authenticated identity on the server side.
AI Analysis
Technical Summary
CVE-2026-54047 describes an improper authentication vulnerability (CWE-287) in Laci Synchroni server versions before 1.2.3. The vulnerability arises because the server relies on the UID field inside the user's local config.json file, which can be manipulated by an attacker to supply an arbitrary UID. The server fails to verify that the OAuth2 authenticated identity matches the requested UID, enabling full impersonation of any user. The patch in version 1.2.3 modifies the AuthorizeOauthAsync method in the SecretKeyAuthenticatorService to ensure the requested UID matches the authenticated identity before issuing session tokens.
Potential Impact
An attacker can fully impersonate any target user by modifying their local config file to supply an arbitrary UID, then logging in. This allows unauthorized actions on behalf of the victim user, potentially compromising user data and system integrity. The vulnerability is critical with a CVSS 4.0 score of 9.2, indicating high impact and ease of exploitation without user interaction or privileges.
Mitigation Recommendations
Upgrade Laci Synchroni server to version 1.2.3 or later, where the vulnerability is fixed. The patch enforces server-side validation that the authenticated OAuth2 identity matches the requested UID, preventing impersonation. No known workarounds exist, so applying the official fix is required.
CVE-2026-54047: CWE-287: Improper Authentication in LaciSynchroni server
Description
Laci Synchroni server versions prior to 1.2.3 contain an improper authentication vulnerability in the OAuth2 login flow. The server trusts a client-side UID value from a local config file without verifying it against the authenticated identity, allowing attackers to impersonate any user. This critical vulnerability has been fixed in version 1.2.3 by enforcing strict binding between the requested UID and the authenticated identity on the server side.
CVSS v4.0
Score 9.2critical
Affected software
LaciSynchroni
server
pkg:github/lacisynchroni/serverRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-54047 describes an improper authentication vulnerability (CWE-287) in Laci Synchroni server versions before 1.2.3. The vulnerability arises because the server relies on the UID field inside the user's local config.json file, which can be manipulated by an attacker to supply an arbitrary UID. The server fails to verify that the OAuth2 authenticated identity matches the requested UID, enabling full impersonation of any user. The patch in version 1.2.3 modifies the AuthorizeOauthAsync method in the SecretKeyAuthenticatorService to ensure the requested UID matches the authenticated identity before issuing session tokens.
Potential Impact
An attacker can fully impersonate any target user by modifying their local config file to supply an arbitrary UID, then logging in. This allows unauthorized actions on behalf of the victim user, potentially compromising user data and system integrity. The vulnerability is critical with a CVSS 4.0 score of 9.2, indicating high impact and ease of exploitation without user interaction or privileges.
Mitigation Recommendations
Upgrade Laci Synchroni server to version 1.2.3 or later, where the vulnerability is fixed. The patch enforces server-side validation that the authenticated OAuth2 identity matches the requested UID, preventing impersonation. No known workarounds exist, so applying the official fix is required.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-06-11T16:57:50.020Z
- Cvss Version
- 4.0
- State
- PUBLISHED
Threat ID: 6aa42d2091cc7f384865fa86
Added to database: 09/11/2026, 16:32:32 UTC
Last enriched: 09/11/2026, 16:46:50 UTC
Last updated: 09/11/2026, 16:51:47 UTC
Views: 4
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