Headline
CVE-2022-24738: Malicious Migration of Claimable Amount through IBC
Evmos is the Ethereum Virtual Machine (EVM) Hub on the Cosmos Network. In versions of evmos prior to 2.0.1 attackers are able to drain unclaimed funds from user addresses. To do this an attacker must create a new chain which does not enforce signature verification and connects it to the target evmos instance. The attacker can use this joined chain to transfer unclaimed funds. Users are advised to upgrade. There are no known workarounds for this issue.
Impact
What kind of vulnerability is it? Who is impacted?
Classification
The vulnerability has been classified as critical with a score of 9.0 (highest). It has the potential to affect and drain unclaimed airdrop funds from Cosmos and Osmosis eligible user addresses.
Disclosure
The attack requires advanced knowledge of the internals of the core and application packages of IBC, IBC relayers, the Cosmos SDK AnteHandler, and the Evmos x/claims module. The step-by-step attack is described below:
- An actor creates a malicious chain with a custom AnteHandler that skips signature verification for transactions, specifically IBC MsgTransfer. This allows the attacker to impersonate any account by setting a custom sender address field of the IBC transfer message.
- The malicious actor then connects this newly created chain via IBC to Evmos and fills the recipient address from the transfer message with an address they control.
- Once the IBC packet containing the Transfer data is relayed to Evmos, it is processed by the claims module IBC middleware. Which migrates the claim records to the recipient address, which is owned by the attacker.
- The attacker then performs two airdrop Actions, claiming up to 75% of the total initial claimable amount.
- The Actor repeats steps 1., 2., and 3. for every address that has unclaimed funds from the airdrop. This automatically claims 75% of the unclaimable amount.
- The malicious actor performs the final Action, claiming 100% of all the user funds.
- Then, the attacker transfers the funds to another chain with a DEX (Osmosis, Cosmos Hub) via IBC.
- Finally, the attacker withdraws the total amount in fiat through a centralized exchange.
Users impacted
No users have suffered the loss of funds as no malicious chains have been connected to Evmos.
Patches
Has the problem been patched? What versions should users upgrade to?
The patch involves defining a list of authorized channels for chains that are connected to Evmos via IBC. This restricts the chains that have the capability of migrating users’ claims records as per the specification. By default, the authorized destination channels are “channel-0” (Osmosis) and “channel-3” (Cosmos Hub).
Please upgrade your mainnet node and validator to v2.0.1 ASAP.
Workarounds
Is there a way for users to fix or remediate the vulnerability without upgrading?
No, the fix for the critical vulnerability is state machine breaking. An upgrade procedure must be coordinated with the nodes running the network.
References
Are there any links users can visit to find out more?
- Claims module spec: evmos.dev/modules/claims
- Cosmos SDK documentation: docs.cosmos.network
- IBC documentation: ibc.cosmos.network
For more information
If you have any questions or comments about this advisory:
- Reach out to the Core Team in Discord
- Open an issue in tharsis/evmos
- Email us at [email protected]
Thanks to the Core IBC team at Interchain GmbH for the secure disclosure of this vulnerability