Only flip BigDecimal exponent if > 0, under assumption it was encoded by CBOR generator < v2.10 with bug FasterXML#139. Assumes all generated BigDecimal values had negative exponents to begin with so not generally applicable to community at large.

Author: msqr

cbor/src/main/java/com/fasterxml/jackson/dataformat/cbor/CBORParser.java

@@ -882,7 +882,11 @@ protected JsonToken _handleTaggedArray(int tag, int len) throws IOException
             _reportError("Unexpected token ("+currentToken()+") as the first part of 'bigfloat' value: should get VALUE_NUMBER_INT");
         }
         // 27-Nov-2019, tatu: As per [dataformats-binary#139] need to change sign here
-        int exp = -getIntValue();
+        //                    if decoding CBOR generated < v2.10
+        int exp = getIntValue();
+        if ( exp < 0 ) {
+          exp = -exp;
+        }
 
         // Should get an integer value; int/long/BigInteger
         if (!_checkNextIsIntInArray("bigfloat")) {

cbor/src/test/java/com/fasterxml/jackson/dataformat/cbor/parse/ParserNumbersTest.java

@@ -361,4 +361,21 @@ public void testBigDecimalType2() throws IOException {
             assertNull(parser.nextToken());
         }
     }
+
+    public void testBigDecimalType3() throws IOException {
+        // Maintain backwards compatibility with < v2.10 where generated CBOR
+        // affected by [dataformats#139]
+        final byte[] spec = new byte[] {
+                (byte) 0xC4,  // tag 4
+                (byte) 0x82,  // Array of length 2
+                0x02,  // int -- 2 (should have been 0x21 for -2)
+                0x19, 0x6a, (byte) 0xb3 // int 27315
+        };
+        try (CBORParser parser = cborParser(spec)) {
+            assertEquals(JsonToken.VALUE_NUMBER_FLOAT, parser.nextToken());
+            assertEquals(NumberType.BIG_DECIMAL, parser.getNumberType());
+            assertEquals(new BigDecimal("273.15"), parser.getDecimalValue());
+            assertNull(parser.nextToken());
+        }
+    }
 }