Failed to decode base64 string – – How to solve this Elasticsearch error

Opster Team

Aug-23, Version: 6.8-8.9

Briefly, this error occurs when Elasticsearch tries to decode a string that is not in valid Base64 format. Base64 is a binary-to-text encoding scheme used to represent binary data in an ASCII string format. If the string is not correctly formatted, the decoding process will fail. To resolve this issue, ensure that the string you’re trying to decode is in valid Base64 format. You can use online tools to validate or convert your string to Base64. Also, check for any leading or trailing whitespaces or special characters that might be causing the issue.

This guide will help you check for common problems that cause the log ” Failed to decode base64 string [{}] – {} ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: plugin.

Log Context

Log “Failed to decode base64 string [{}] – {}” classname is
We extracted the following from Elasticsearch source code for those seeking an in-depth context :

    protected byte[] decodeBase64(String content) {
        try {
            return Base64.getDecoder().decode(content.replaceAll("\s+"; ""));
        } catch (IllegalArgumentException e) {
  "Failed to decode base64 string [{}] - {}"; content; e.toString());
            throw samlException("SAML message cannot be Base64 decoded"; e);

    protected byte[] inflate(byte[] bytes) {


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