CVE-2026-87785 in Syncope
Summary
by MITRE • 09/14/2026
Authentication bypass by spoofing vulnerability in Apache Syncope.
When the configured JWKS settings for internal JWT authentication are disclosed (at least protocol and key), an attacker can spoof another user's privileges after completing a successful authentication and obtaining a valid JWT.
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 in Apache Syncope represents a critical authentication bypass mechanism rooted in the improper handling of JSON Web Token (JWT) validation and key management configurations. Specifically, the flaw arises when the Java Web Key Set (JWKS) settings used for internal JWT authentication are inadvertently disclosed or made accessible to unauthorized parties. In secure identity management systems like Apache Syncope, JWKS serves as a repository for public keys required to verify the digital signatures of JWTs issued by trusted authorities. When these configuration details, including the protocol endpoints and cryptographic key material, are exposed, it fundamentally undermines the integrity checks that rely on asymmetric cryptography. An attacker who gains access to this sensitive information can effectively replicate the trust relationship established between the identity provider and the application server, thereby creating a pathway for privilege escalation without possessing valid credentials through legitimate means.
The operational impact of this vulnerability is severe because it allows an adversary to forge authentication tokens that appear authentic to the system. Once an attacker has completed a successful initial authentication—perhaps by exploiting a separate lower-severity flaw or using stolen low-privilege credentials—they can obtain a valid JWT. With knowledge of the JWKS configuration and keys, the attacker can then construct new JWTs signed with the compromised key material but claiming different user identities or elevated privileges. This process effectively bypasses the authentication layer entirely for subsequent requests, as the system validates the forged token against the known public key and accepts it as legitimate. Consequently, an attacker can impersonate any user within the system, including administrators, leading to unauthorized access to sensitive data, modification of configuration settings, and potential full compromise of the underlying infrastructure managed by Apache Syncope.
This vulnerability aligns with CWE-287, which describes Improper Authentication, specifically focusing on scenarios where authentication mechanisms are bypassed through spoofing or credential manipulation. Furthermore, it maps directly to MITRE ATT&CK technique T1651, Cloud Service Session Hijacking, as the exploitation involves manipulating session tokens (JWTs) that maintain state and identity within a cloud-native or web-based application environment. The root cause lies in CWE-209, which relates to the Generation of Error Message Containing Sensitive Information, although here it extends beyond mere error messages to include the exposure of critical cryptographic configuration parameters necessary for token verification. This misconfiguration violates fundamental security principles regarding the separation of sensitive operational data from publicly accessible endpoints and the principle of least privilege in key management.
To mitigate this risk, organizations must immediately upgrade Apache Syncope to version 4.0.8 or 4.1.3, as these releases contain specific patches that address the improper exposure of JWKS settings. In addition to upgrading, administrators should audit their deployment configurations to ensure that internal API endpoints and metadata URLs are not exposed through reverse proxies, load balancers, or direct server access without strict IP-based restrictions. It is crucial to implement network-level controls such as firewall rules or security groups that restrict access to authentication-related services exclusively to trusted application servers and management networks. Regular vulnerability assessments should include checks for misconfigured identity providers where sensitive cryptographic material might be inadvertently served over HTTP or accessible via unauthenticated GET requests, ensuring that the confidentiality of signing keys remains intact and that JWT validation relies on secure, internal-only communication channels.