.eth registrar controller can shorten the duration of registered names

Ethereum Name Service (ENS) is a distributed, open, and extensible naming system based on the Ethereum blockchain. According to the documentation, controllers are allowed to register new domains and extend the expiry of existing domains, but they cannot change the ownership or reduce the expiration time of existing domains. However, a preliminary analysis suggests that an attacker-controlled controller may be able to reduce the expiration time of existing domains due to an integer overflow in the renew function. The vulnerability resides @ensdomains/ens-contracts prior to version 0.0.22.

If successfully exploited, this vulnerability would enable attackers to force the expiration of any ENS record, ultimately allowing them to claim the affected domains for themselves. Currently, it would require a malicious DAO to exploit it. Nevertheless, any vulnerability present in the controllers could potentially render this issue exploitable in the future. An additional concern is the possibility of renewal discounts. Should ENS decide to implement a system that offers unlimited .eth domains for a fixed fee in the future, the vulnerability could become exploitable by any user due to the reduced attack cost.

Version 0.0.22 contains a patch for this issue. As long as registration cost remains linear or superlinear based on registration duration, or limited to a reasonable maximum (eg, 1 million years), this vulnerability could only be exploited by a malicious DAO. The interim workaround is thus to take no action.