0.16.3 was recently released, and if you’re running a node and haven’t already updated, we recommend you do so as soon as possible. A bug fixed in 0.16.3 is more severe than was previously made public. You can download 0.16.3 from bitcoin.org. As always, make sure that you verify the authenticity of the download with GPG using the signing key and release signatures.
Stored funds are not at risk, and never were at risk. Even if the bug had been exploited to its full extent, the theoretical damage to stored funds would have been rolled back, exactly as it was in the value overflow incident. However, there is currently a small risk of a chain split. In a chain split, transactions could be reversed long after they are fully confirmed. Therefore, for the next week or so you should consider there to be a small possibility of any transaction with less than 200 confirmations being reversed.
Below is a summary of required action items:
You should not run any version of Bitcoin Core other than 0.16.3. Older versions should not exist on the network. If you know anyone who is running an older version, tell them to upgrade it as soon as possible.
It’s not necessary to immediately upgrade older versions if they are currently shut down. Cold-storage wallets are safe.
For approximately the next week, consider transactions with fewer than 200 confirmations to have a low probability of being reversed (whereas usually there would be essentially zero probability of transactions having six or more confirmations being reversed).
Please watch for further news. If a chain split happens, additional action may be required.
More information: CVE-2018-17144 Full Disclosure