CVE-2026-87802 in Syncope
Summary
by MITRE • 09/14/2026
Improper verification of cryptographic signature vulnerability in Apache Syncope.
When SRA is configured for OAuth 2.0 without JWKS set URI assigned, an attacker can forge arbitrary JWTs to impersonate any user identity and permissions, gaining full access to services proxied by SRA.
This issue affects Apache Syncope: from 3.0.0-M0 through 3.0.16, from 4.0.0-M0 through 4.0.7, from 4.1.0-M0 through 4.1.2.
Users are recommended to upgrade to version 4.0.8 / 4.1.3, which fix this issue.
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Analysis
by VulDB Data Team • 09/14/2026
The vulnerability identified in Apache Syncope represents a critical failure in the verification of cryptographic signatures within its Secure Resource Access (SRA) component when configured for OAuth 2.0 authentication flows. This flaw specifically manifests under conditions where the JSON Web Key Set (JWKS) URI is not properly assigned or configured during the setup process. In standard OAuth 2.0 implementations utilizing JWTs, the relying party must validate the signature of every incoming token against a trusted public key to ensure integrity and authenticity. The absence of this validation step creates a severe security gap that allows attackers to bypass authentication mechanisms entirely by crafting arbitrary JSON Web Tokens with forged signatures or no signatures at all.
From a technical perspective, the core issue lies in the application's logic for handling JWTs when JWKS configuration is missing. Instead of rejecting tokens without valid cryptographic proof of origin, the vulnerable versions of Apache Syncope accept these malformed or unsigned tokens as legitimate credentials. This behavior effectively neutralizes the security guarantees provided by OAuth 2.0 and JSON Web Token standards. An attacker can exploit this by generating a JWT with arbitrary claims, such as setting the subject to an administrative user role or granting themselves elevated permissions that were not originally assigned. Since the system fails to verify whether the token was actually signed by the trusted identity provider, it treats these forged tokens as authentic session identifiers.
The operational impact of this vulnerability is severe and potentially catastrophic for organizations relying on Apache Syncope for centralized identity management. Successful exploitation allows an attacker to impersonate any user within the ecosystem, including high-privilege administrators. This leads to a complete compromise of confidentiality, integrity, and availability depending on the actions taken by the attacker once authenticated. The adversary gains full access to all services proxied through the SRA component, enabling unauthorized data exfiltration, modification of critical system configurations, or deployment of further malicious payloads within the internal network perimeter. This scenario aligns with CWE-347 Improper Verification of Cryptographic Signature and is consistent with ATT&CK technique T1621 Multi-Factor Authentication Request Interception where trust in authentication tokens is abused to bypass access controls.
To mitigate this risk, immediate action is required for all affected deployments. The recommended remediation strategy involves upgrading Apache Syncope to version 4.0.8 or later, specifically targeting versions 4.1.3 and above which contain the necessary patches to enforce strict signature verification regardless of JWKS URI configuration status. Organizations should also audit their current configurations to ensure that JWKS URIs are correctly defined for all OAuth 2.0 clients where applicable. Additionally implementing defense-in-depth measures such as monitoring for unusual authentication patterns or tokens with unexpected claims can provide an additional layer of detection against exploitation attempts while the upgrade process is being executed across the infrastructure.