In Couchbase Server 4.6.3 and 5.5.0, secondary indexing encodes the entries to be indexed using collatejson. When index entries contain certain characters like \t, <, >, it caused buffer overrun as encoded string would be much larger than accounted for, causing indexer service to crash and restart. This has been remedied in versions 5.1.2 and 5.5.2 to ensure buffer always grows as needed for any input.