Upgrade Now: Litecoin Core v0.21.5.6 Delivers Critical MWEB Security Fixes Before Soft Fork Next Week

The Litecoin development team have released another Litecoin Core update, v0.21.5.6.

Just a couple of months ago, v0.21.5.5 was released to address recent network and MWEB-related issues.

This is an urgent maintenance release that strengthens MWEB transaction,

block, and P2P-service validation. Upgrading is strongly recommended for all

users. Miners, pools, and MWEB service operators should upgrade before the

activation height described below.

How to upgrade:

To upgrade on Linux, download the release with this command:

Verify the hash of the file matches the official release. For Linux, the SHA256 hash is:

3c0a217651a431ef446641669a0b74ce7dbcd9b9ed1a118fc830b8f6779ee83f

Run the command to check the file hash:

Now extract the release:

Once extracted, install it:

Then start your node:

Another round of bugs squashed. MWEB hardening continues.

At mainnet height 3,154,440, nodes running 0.21.5.6 will reject an MWEB

block containing a kernel that signals a pegout while carrying an empty pegout

list. This is a soft-forking consensus rule. The height is approximately one

week (4,032 blocks) after height 3,150,408.

Valid wallets and miners do not create this encoding. All miners and pools

should upgrade before activation to avoid producing blocks that upgraded nodes

will reject (b250b01).

Changes in Litecoin Core v0.21.5.6:

MWEB security and reliability

• Added a node-wide limit for expensive MWEB light-client service requests.

• This protects getmwebleafset and getmwebutxos from resource exhaustion

• across reconnecting peers while retaining normal light-client synchronization

• behavior (cb65fc5, f24dec1).

• Added relay-policy limits for MWEB transaction weight and input count before

• expensive cryptographic verification. Oversized MWEB transactions are no

• longer admitted to the mempool (109ed13).

• Reject invalid MWEB output public keys and safely ignore malformed MWEB

• output data during wallet scanning (cfdfcf5).

• Improved handling of mutated MWEB block data: descendants of a discarded

• mutated block remain processable, and peers that deliver invalid MWEB data

• through compact blocks are discouraged (4dd6aee, 136695e).

• Standard relay policy now rejects kernels that signal a pegout but contain no

• pegouts (67580d6).

  
  

Consensus change

• At mainnet height 3,154,440, nodes running 0.21.5.6 will reject an MWEB block containing a kernel that signals a pegout while carrying an empty pegout list. This is a soft-forking consensus rule. The height is approximately one week (4,032 blocks) after height 3,150,408.

  
  

• Valid wallets and miners do not create this encoding. All miners and pools should upgrade before activation to avoid producing blocks that upgraded nodes will reject (b250b01).

  
  

Mining

• Block construction now enforces the MWEB consensus input limit, preventing

  miners from assembling oversized MWEB input sets (dc72334).

  
  

Tests

• Expanded MWEB P2P, mining, transaction-policy, and malformed-data regression

  coverage.

Checksums of software on github repo.

Thanks to David Burkett and DeltaXV.

Sources:

• Litecoin Core v0.21.5.6 release

  https://github.com/litecoin-project/litecoin/releases/tag/v0.21.5.6

• Litecoin

  https://litecoin.org/

• X social

  https://x.com/litecoin