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CVE-2026-88920 – SAML Authentication Bypass – Apache WSS4J (versions before 2.4.4, 3.0.0–3.0.5, 4.0.

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Summary

CVE-2026-88920 is a critical authentication bypass vulnerability in Apache WSS4J, a widely used Java library implementing the WS-Security standard for securing SOAP web services. The flaw resides in WSS4J’s DOM security processor and allows unauthenticated remote attackers to forge authenticated SOAP messages by submitting a crafted, unsigned SAML "sender-vouches" assertion that contains an attacker-controlled key. The issue carries a CVSS v3.1 base score of 9.8 (Critical) and requires no privileges or user interaction to exploit.

Technical details

  • Root cause: The DOM security processor in Apache WSS4J improperly validates SAML "sender-vouches" assertions, failing to require that the assertion be signed or that the associated key material be trustworthy.
  • Trigger conditions: An attacker crafts a SOAP message containing an unsigned SAML sender-vouches assertion embedding an attacker-controlled key, then submits it to a service relying on WSS4J for WS-Security SAML token validation.
  • Attack vector: Network-based (AV:N); no authentication or user interaction is required, making the vulnerability exploitable by any remote, unauthenticated party able to reach the affected web service endpoint.
  • Impact: Successful exploitation allows an attacker to forge authenticated SOAP messages, effectively bypassing authentication controls that rely on WSS4J’s SAML token processing. This can lead to full compromise of confidentiality, integrity, and availability of the affected application, as reflected in the CVSS impact metrics (C:H/I:H/A:H).

Affected software

  • Apache WSS4J (org.apache.wss4j:wss4j-ws-security-dom) versions 4.0.0 through 4.0.1
  • Apache WSS4J versions 3.0.0 through 3.0.5
  • Apache WSS4J versions prior to 2.4.4

Severity

  • CVSS v3.1 Base Score: 9.8 (Critical)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Mitigation and recommended actions

  • Immediate: Upgrade Apache WSS4J to a fixed version corresponding to your release line:
    • 4.0.x users → upgrade to 4.0.2
    • 3.0.x users → upgrade to 3.0.6
    • Earlier (2.x) users → upgrade to 2.4.4
  • If immediate patching is not possible: Review and restrict services that accept SAML sender-vouches assertions over WS-Security, ensure network-level access controls limit exposure of affected SOAP endpoints to trusted sources, and monitor for anomalous or malformed SAML assertions in inbound SOAP traffic until the patch can be applied.
  • After upgrading, audit authentication logs for evidence of forged or anomalous SAML-authenticated sessions predating remediation.

References

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