diff -up ./java/org/apache/coyote/http2/HpackDecoder.java.orig ./java/org/apache/coyote/http2/HpackDecoder.java
--- ./java/org/apache/coyote/http2/HpackDecoder.java.orig	2020-12-18 17:16:34.502408251 +0800
+++ ./java/org/apache/coyote/http2/HpackDecoder.java	2020-12-18 17:22:27.675912403 +0800
@@ -72,8 +72,6 @@ public class HpackDecoder {
     private volatile boolean countedCookie;
     private volatile int headerSize = 0;
 
-    private final StringBuilder stringBuilder = new StringBuilder();
-
     HpackDecoder(int maxMemorySize) {
         this.maxMemorySizeHard = maxMemorySize;
         this.maxMemorySizeSoft = maxMemorySize;
@@ -222,19 +220,17 @@ public class HpackDecoder {
         if (huffman) {
             return readHuffmanString(length, buffer);
         }
+	StringBuilder stringBuilder = new StringBuilder(length);
         for (int i = 0; i < length; ++i) {
             stringBuilder.append((char) buffer.get());
         }
-        String ret = stringBuilder.toString();
-        stringBuilder.setLength(0);
-        return ret;
+        return stringBuilder.toString();
     }
 
     private String readHuffmanString(int length, ByteBuffer buffer) throws HpackException {
+	StringBuilder stringBuilder = new StringBuilder(length);
         HPackHuffman.decode(buffer, length, stringBuilder);
-        String ret = stringBuilder.toString();
-        stringBuilder.setLength(0);
-        return ret;
+        return stringBuilder.toString();
     }
 
     private String handleIndexedHeaderName(int index) throws HpackException {
diff -up ./webapps/docs/changelog.xml.orig ./webapps/docs/changelog.xml
--- webapps/docs/changelog.xml.orig	2020-12-18 17:25:29.287714327 +0800
+++ webapps/docs/changelog.xml	2020-12-18 17:30:42.780824782 +0800
@@ -159,6 +159,9 @@
         frame in the input buffer. (markt)
       </fix>
     </changelog>
+      <fix>
+        <bug>64830</bug>: Fix concurrency issue in HPACK decoder. (markt)
+      </fix>
   </subsection>
   <subsection name="Jasper">
     <changelog>