Apache WSS4J stores the Nonce of each accepted UsernameToken as raw base64 text to prevent replay attacks. However, because the authentication process decodes the base64 text and uses the underlying bytes, an attacker can resend a captured authenticated request with a modified base64 Nonce (e.g., adding a space) that still decodes to the same bytes. This causes the replay cache to fail to recognize the token as a replay, allowing reuse of the token until it expires. This vulnerability affects deployments with a nonce replay cache configured (such as Apache CXF by default) and only impacts tokens using password digest authentication. The fix involves keying the replay cache on the decoded Nonce bytes rather than the raw base64 text.

An attacker who captures an authenticated request can replay it by modifying the base64 encoding of the Nonce without invalidating the password digest verification. This allows reuse of the UsernameToken on requests of the attacker's choosing until the token expires, potentially bypassing replay protections. The vulnerability affects systems using nonce replay caches and password digest tokens, potentially undermining authentication integrity.

Users should upgrade Apache WSS4J to versions 4.0.2, 3.0.6, or 2.4.4 where the replay cache keys on the decoded Nonce bytes, preventing this replay attack. No other mitigation is indicated or required once these versions are deployed.