CVE-2021-41272 (published 2021-12-13T21:15Z)

Besu is an Ethereum client written in Java. Starting in version 21.10.0, changes in the implementation of the SHL, SHR, and SAR operations resulted in the introduction of a signed type coercion error in values that represent negative values for 32 bit signed integers. Smart contracts that ask for shifts between approximately 2 billion and 4 billion bits (nonsensical but valid values for the operation) will fail to execute and hence fail to validate. In networks where vulnerable versions are mining with other clients or non-vulnerable versions this will result in a fork and the relevant transactions will not be included in the fork. In networks where vulnerable versions are not mining (such as Rinkeby) no fork will result and the validator nodes will stop accepting blocks. In networks where only vulnerable versions are mining the relevant transaction will not be included in any blocks. When the network adds a non-vulnerable version the network will act as in the first case. Besu 21.10.2 contains a patch for this issue. Besu 21.7.4 is not vulnerable and clients can roll back to that version. There is a workaround available: Once a transaction with the relevant shift operations is included in the canonical chain, the only remediation is to make sure all nodes are on non-vulnerable versions.

Severity: MEDIUM
CVSS v2 base score: 5.0 (AV:N/AC:L/Au:N/C:N/I:N/A:P)
CVSS v3 base score: 7.5, HIGH (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

Weakness information:
cwe_id: CWE-681
cwe_name: Incorrect Conversion between Numeric Types
description: When converting from one data type to another, such as long to integer, data can be omitted or translated in a way that produces unexpected values. If the resulting values are used in a sensitive context, then dangerous behaviors may occur.
extended_description: 
            
            
            
         
         

Fix information:
repo_url: https://github.com/hyperledger/besu
commit_details: repo_url: https://github.com/hyperledger/besu
author: Danno Ferrin
author_date: 2021-11-11 07:56:53-07:00
msg: Shift Optimization (#3039)

Reduce shift calculations to shifts that may have an actual result.

Signed-off-by: Danno Ferrin <danno.ferrin@gmail.com>
repository: repo_url: https://github.com/hyperledger/besu
repo_name: hyperledger/besu
description: An enterprise-grade Java-based, Apache 2.0 licensed Ethereum client https://wiki.hyperledger.org/display/besu
repo_language: Java
owner: hyperledger
file_changes: filename: SarOperation.java
change_type: ModificationType.MODIFY
diff: @@ -44,7 +44,7 @@ public class SarOperation extends AbstractFixedCostOperation {
     } else {
       final int shiftAmountInt = shiftAmount.toInt();
 
-      if (shiftAmountInt >= 256) {
+      if (shiftAmountInt >= 256 || shiftAmountInt < 0) {
         frame.pushStackItem(negativeNumber ? ALL_BITS : UInt256.ZERO);
       } else {
         // first perform standard shift right.

programming_language: Java
filename: ShlOperation.java
change_type: ModificationType.MODIFY
diff: @@ -40,7 +40,7 @@ public class ShlOperation extends AbstractFixedCostOperation {
       final int shiftAmountInt = shiftAmount.toInt();
       final Bytes value = leftPad(frame.popStackItem());
 
-      if (shiftAmountInt >= 256) {
+      if (shiftAmountInt >= 256 || shiftAmountInt < 0) {
         frame.pushStackItem(UInt256.ZERO);
       } else {
         frame.pushStackItem(value.shiftLeft(shiftAmountInt));

programming_language: Java
filename: ShrOperation.java
change_type: ModificationType.MODIFY
diff: @@ -40,7 +40,7 @@ public class ShrOperation extends AbstractFixedCostOperation {
       final int shiftAmountInt = shiftAmount.toInt();
       final Bytes value = leftPad(frame.popStackItem());
 
-      if (shiftAmountInt >= 256) {
+      if (shiftAmountInt >= 256 || shiftAmountInt < 0) {
         frame.pushStackItem(UInt256.ZERO);
       } else {
         frame.pushStackItem(value.shiftRight(shiftAmountInt));

programming_language: Java