Ethereum Core

The Ethereum Core Developers and the Ethereum Security Community were made aware of the potential Constantinople-related issues identified by ChainSecurity on January 15, 2019. We are investigating any potential vulnerabilities and will follow with updates in this blog post and across social media channels.
Out of an abundance of caution, key stakeholders around the Ethereum community have determined that the best course of action will be to delay the planned Constantinople fork that would have occurred at block 7,080,000 on January 16, 2019.
This will require anyone running a node (node operators, exchanges, miners, wallet services, etc...) to update to a new version of Geth or Parity before block 7,080,000. Block 7,080,000 will occur in approximately 32 hours from the time of this publishing or at approximately January 16, 8:00pm PT / January 16, 11:00pm ET / January 17, 4:00am GMT.

What You Need To Do

If you are a person who simply interacts with Ethereum (you do not run a node), you do not need to do anything.

Miners, Exchanges, Node Operators:

• Update your Geth and/or Parity instances when they are released.
• These releases are not released yet. We will update this post when they are available.
• Links and version numbers and instructions will be provided here when they are available.
• We expect to have updated releases in 3-4 hours from the time this blog is published.

Geth

• Upgrade to 1.8.21 , OR
• Downgrade to Geth 1.8.19, OR
• Remain on 1.8.20, but use the switch '--override.constantinople=9999999' to postpone the Constantinople fork indefinitely.

Parity

• Upgrade to Parity Ethereum 2.2.7-stable (recommended)
• Upgrade to Parity Ethereum 2.3.0-beta
• Downgrade to Parity Ethereum 2.2.4-beta (not recommended)

Everyone Else:

Ledger, Trezor, Safe-T, Parity Signer, WallEth, Paper Wallets, MyCrypto, MyEtherWallet and other users or token holders that do not participate in the network by syncing and running a node.