SAML message cannot be Base64 decoded – How to solve this Elasticsearch exception

Opster Team

August-23, Version: 7.7-8.9

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Briefly, this error occurs when Elasticsearch fails to decode a SAML (Security Assertion Markup Language) message because it’s not correctly encoded in Base64. This could be due to a faulty SAML assertion from the identity provider or a misconfiguration in Elasticsearch. To resolve this issue, you can: 1) Verify the SAML assertion from your identity provider to ensure it’s correctly Base64 encoded. 2) Check your Elasticsearch SAML configuration settings for any errors. 3) If the problem persists, consider reconfiguring your SAML settings or contacting your identity provider for further assistance.

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This guide will help you check for common problems that cause the log ” SAML message cannot be Base64 decoded ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: plugin.

Log Context

Log “SAML message cannot be Base64 decoded” class name is We extracted the following from Elasticsearch source code for those seeking an in-depth context :

 private byte[] decodeBase64(String content) {
 try {
 return Base64.getDecoder().decode(content.replaceAll("\s+"; ""));
 } catch (IllegalArgumentException e) {"Failed to decode base64 string [{}] - {}"; content; e);
 throw new ElasticsearchSecurityException("SAML message cannot be Base64 decoded"; RestStatus.BAD_REQUEST; e);
 }  private byte[] inflate(byte[] bytes) {
 Inflater inflater = new Inflater(true);


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