CVE-2026-87802 Overview
CVE-2026-87802 is an improper verification of cryptographic signature vulnerability [CWE-347] in Apache Syncope. The flaw exists in the Secure Remote Access (SRA) component when configured for OAuth 2.0 without a JSON Web Key Set (JWKS) set URI assigned. Attackers can forge arbitrary JSON Web Tokens (JWTs) to impersonate any user identity and permissions. Successful exploitation grants full access to services proxied by SRA.
The vulnerability affects Apache Syncope versions 3.0.0-M0 through 3.0.16, 4.0.0-M0 through 4.0.7, and 4.1.0-M0 through 4.1.2. The Apache Syncope project recommends upgrading to version 4.0.8 or 4.1.3.
Critical Impact
Remote unauthenticated attackers can forge JWTs to impersonate any user and gain full access to services proxied through Apache Syncope SRA.
Affected Products
- Apache Syncope 3.0.0-M0 through 3.0.16
- Apache Syncope 4.0.0-M0 through 4.0.7
- Apache Syncope 4.1.0-M0 through 4.1.2
Discovery Timeline
- 2026-09-14 - CVE-2026-87802 published to NVD
- 2026-09-14 - Last updated in NVD database
Technical Details for CVE-2026-87802
Vulnerability Analysis
Apache Syncope provides identity management and Secure Remote Access (SRA) for proxying services behind authentication. When SRA is configured to authenticate users via OAuth 2.0, the deployment can optionally specify a JWKS set URI used to fetch the trusted public keys required to verify inbound JWT signatures.
When the JWKS set URI is not assigned, SRA fails to properly verify the cryptographic signature on incoming JWTs. An attacker can craft an arbitrary token containing any claims, including elevated identity and permissions. SRA accepts the forged token and grants the attacker access to any service proxied by the gateway.
The issue is network-reachable and requires no prior authentication or user interaction, making it directly exploitable against internet-exposed SRA endpoints.
Root Cause
The root cause is missing enforcement of JWT signature verification when the OAuth 2.0 configuration omits a JWKS set URI. Rather than rejecting tokens whose signatures cannot be validated against a trusted key, SRA processes the token claims as authoritative. This behavior maps to [CWE-347: Improper Verification of Cryptographic Signature].
Attack Vector
An unauthenticated remote attacker sends an HTTP request to an SRA endpoint with a self-signed or unsigned JWT bearer token. The token contains arbitrary subject, role, and permission claims chosen by the attacker. Because SRA does not verify the signature, it treats the impersonated identity as valid and forwards the request to downstream proxied services with the attacker's chosen privileges.
No verified public exploit code is available for CVE-2026-87802. See the Apache Thread Discussion and OpenWall OSS-Security Update for advisory details.
Detection Methods for CVE-2026-87802
Indicators of Compromise
- Authentication events in SRA logs referencing user identities that did not originate from the expected identity provider.
- JWT bearer tokens presented to SRA endpoints with signatures that do not chain to any configured trusted key.
- Access to proxied services from source IPs that have not previously completed an interactive OAuth 2.0 flow.
- Requests with anomalous claim combinations, such as high-privilege roles assigned to previously unseen sub values.
Detection Strategies
- Audit SRA OAuth 2.0 configuration and flag any deployment where the JWKS set URI is empty or unset.
- Correlate SRA access logs with identity provider issuance logs to identify tokens accepted by SRA that were never issued upstream.
- Alert on JWT alg header values of none or on unexpected signing algorithms reaching SRA endpoints.
Monitoring Recommendations
- Forward Syncope SRA access and authentication logs to a centralized analytics platform for cross-source correlation.
- Baseline normal JWT issuers, audiences, and subject patterns, then alert on deviations.
- Monitor egress from services proxied by SRA for unusual data access following authentication events.
How to Mitigate CVE-2026-87802
Immediate Actions Required
- Upgrade Apache Syncope to version 4.0.8 or 4.1.3 as recommended by the project maintainers.
- Inventory all SRA deployments and confirm whether OAuth 2.0 is configured without a JWKS set URI.
- Rotate any credentials or session tokens for services proxied by SRA that may have been accessed during the exposure window.
- Review SRA and downstream service logs for evidence of forged token usage.
Patch Information
The Apache Syncope project has released fixed versions 4.0.8 and 4.1.3 that address CVE-2026-87802. Deployments on the 3.0.x branch should plan migration to a supported fixed release. Refer to the Apache Thread Discussion for the official advisory.
Workarounds
- Configure a valid JWKS set URI in the SRA OAuth 2.0 configuration so that inbound JWT signatures are verified against trusted keys.
- Restrict network exposure of SRA endpoints to trusted networks or identity provider ranges until patches are applied.
- Place SRA behind a reverse proxy or web application firewall that validates JWT signatures before requests reach Syncope.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
