MetaMask Snap Audit Report For Polkadot

Management Summary

Polkadot contacted Sayfer Security in order to perform a security audit on Polkadot’s Metamask Snap application in August 2023.

Before assessing the above services, we held a kickoff meeting with the technical team and received an overview of the system and the goals for this research.

Over the research period of 2 weeks, we discovered 5 vulnerabilities across the snap’s codebase.

In conclusion, several fixes should be implemented following the report, but the system’s security posture is competent.

Risk Methodology

At Sayfer, we are committed to delivering the highest quality penetration testing to our clients. That’s why we have implemented a comprehensive risk assessment model to evaluate the severity of our findings and provide our clients with the best possible recommendations for mitigation.

Our risk assessment model is based on two key factors: IMPACT and LIKELIHOOD. Impact refers to the potential harm that could result from an issue, such as financial loss, reputational damage, or a non-operational system. Likelihood refers to the probability that an issue will occur, taking into account factors such as the complexity of the attack and the number of potential attackers.

By combining these two factors, we can create a comprehensive understanding of the risk posed by a particular issue and provide our clients with a clear and actionable assessment of the severity of the issue. This approach allows us to prioritize our recommendations and ensure that our clients receive the best possible advice on how to protect their business.

Risk is defined as follows:

Security Evaluation Methodology

Sayfer uses OWASP WSTG as our technical standard when reviewing web applications. After gaining a thorough understanding of the system we decided which OWASP tests are required to evaluate the system.

Security Assessment

After understanding and defining the scope, performing threat modeling, and evaluating the correct tests required in order to fully check the application for security flaws, we performed our security assessment.

Issue Table Description

Issue title

Description

Here we provide a brief description of the issue and how it formed, the steps we made to find or exploit it, along with proof of concept (if present), and how this issue can affect the product or its users.

Mitigation

Suggested resolving options for this issue and links to advised sites for further remediation.

Security Assessment Findings

RPC URLs are defined as wsRpcUrl while using HTTP

Description

The RPC URLs of individual protocols have been changed in the latest version of the snap. HTTP (http://) is used instead of WebSocket (wss://).

This is unexpected, because the official Polkadot documentation indicates only websocket addresses in their resources. Additionally, in many places in the code, variable names still contain the ws prefix, such as wsRpcurl.

predefined.ts:

wsRpcUrl: 'https: /

wsRpcUrl: 'https: /kusama-rpc.polkadot.io/'
{...}
wsRpcUrl: 'https: /westend-rpc.polkadot.io/'
{...}
wsRpcUrl: 'https: /rpc.polkadot.io/'

Mitigation

Make sure that the HTTP protocol is supposed to be used. If it is, change the official documentation to reflect this, and modify the relevant variable names.

Conformations for Key Features are not Handled When Rejected

Description

For key Snap functionalities (such as displaying the private key or signing of a message), dialogs are displayed for the user to confirm whether they are aware of what they are accepting. If the user confirms the transaction, it is executed. The converse, when the user rejects the transaction, is not handled at all.

exportSeed(SnapsGlobalObject), notice how there is no else block

if (confirmation) {
    const bip44Node = (await snap.request({
    method: "snap_getBip44Entropy",
    params: { coinType: kusamaCoinType },
})) as JsonBIP44CoinTypeNode;

signPayloadJSON(SnapsGlobalObject, ApiPromise, SignerPayloadJSON)

if (confirmation) {
    const extrinsic = api.registry.createType('ExtrinsicPayload', payload, { version: payload.version });
    return extrinsic.sign(keyPair);
}

signPayloadRaw(SnapsGlobalObject, ApiPromise, SignerPayloadRaw)

if (confirmation) {
    const signedBytes = keyPair.sign(hexToU8a(payload.data));
    return {
    signature: u8aToHex(signedBytes)
};

Unfortunately, since the automated tests did not work, we could not definitively verify and confirm this scenario.

Mitigation

Handle the else case, where the user rejects the transaction, in which case an appropriate error should be displayed.

No Confirmation Dialogue when Sending

Description

When signing messages or displaying the private key, the snap displays a dialog box asking the user if they’re sure they want to proceed. However, no such confirmation dialogue is displayed when sending.

Mitigation

Implement a dialogue box asking the user to confirm the transaction.

enablePolkadotSnap Returns an Error When Using the Default networkName

Description

It has been noticed that despite selecting Westend as the default network in snap/src/configuration/predefined.ts, if the adapter executes its only exposed function, enablePolkadotSnap(), without specifying config.networkName, then an error will be returned.

This is inconsistent with Snap’s assumptions, described among others in the README.md of the adapter, which indicates that specifying a configuration will override the default one.

packages/snap/src/configuration/predefined.ts; lines 13-22, 35

export const westendConfiguration: SnapConfig = {
    addressPrefix: 42,
    networkName: "westend",
    unit: {
        decimals: 12,
        image: "https: /svgshare.com/i/L2d.svg",
        symbol: "WND",
    },
    wsRpcUrl: "wss: /westend-rpc.polkadot.io/",
};
[ .]
export const defaultConfiguration: SnapConfig = westendConfiguration;

packages/snap/src/configuration/predefined.ts; lines 27-29

if (!config.networkName) {
throw new Error("Configuration must at least define network type");
}

Mitigation

Judging by the documentation and by the code in predefined.ts, this error should not be returned and Westend should be used. Conversely, Westend should not be set as the default and the documentation amended to reflect that.

Non-Working Demo

Description

According to the documentation, the command yarn install & yarn run demo should run a working demo of Snap, allowing you to install it and use the various features. Unfortunately, during installation, the browser console returned an error. Thus, the verification of Snap as a “living organism” was impossible}

Mitigation

We suggest bringing Snap to a usable state, and then conducting in-depth tests on real transactions with the Polkadot network.