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chore: add prototype pollution guards to setState and SnapController #3719

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chore: add prototype pollution guards to setState and SnapController #3719

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25 changes: 18 additions & 7 deletions packages/snaps-controllers/src/snaps/SnapController.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -3943,17 +3943,26 @@ export class SnapController extends BaseController<
const { conversions: requestedConversions } = requestedParams;

const filteredConversionRates = requestedConversions.reduce<
Record<CaipAssetType, Record<CaipAssetType, AssetConversion>>
Map<CaipAssetType, Map<CaipAssetType, AssetConversion>>
>((accumulator, conversion) => {
const rate = conversionRates[conversion.from]?.[conversion.to];
// Only include rates that were actually requested.
if (rate) {
accumulator[conversion.from] ??= {};
accumulator[conversion.from][conversion.to] = rate;
if (!accumulator.has(conversion.from)) {
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@FrederikBolding FrederikBolding Nov 5, 2025

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The results processed in this function come from BaseSnapExecutor, where the result is passed through getSafeJson:

snaps/packages/snaps-execution-environments/src/common/BaseSnapExecutor.ts

Line 199 in ab34f97

return getSafeJson(result);

This function eliminates any disallowed properties like __proto__

accumulator.set(conversion.from, new Map());
}
accumulator.get(conversion.from).set(conversion.to, rate);
}
return accumulator;
}, {});
return { conversionRates: filteredConversionRates };
}, new Map());
// Convert nested Maps into plain objects for return value compatibility.
const conversionRatesObj = Object.fromEntries(
Array.from(filteredConversionRates.entries()).map(([fromKey, toMap]) => [
fromKey,
Object.fromEntries(toMap.entries()),
]),
);
return { conversionRates: conversionRatesObj };
}

/**
Expand All @@ -3980,11 +3989,13 @@ export class SnapController extends BaseController<
const result = marketData[assets.asset]?.[assets.unit];
// Only include rates that were actually requested.
if (result) {
accumulator[assets.asset] ??= {};
if (!accumulator[assets.asset]) {
accumulator[assets.asset] = Object.create(null);
}
accumulator[assets.asset][assets.unit] = result;
}
return accumulator;
}, {});
}, Object.create(null));
return { marketData: filteredMarketData };
}

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10 changes: 8 additions & 2 deletions packages/snaps-rpc-methods/src/permitted/setState.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -260,9 +260,15 @@ export function set(

for (let i = 0; i < keys.length; i++) {
const currentKey = keys[i];
if (FORBIDDEN_KEYS.includes(currentKey)) {
// Explicitly block prototype pollution keys
if (
FORBIDDEN_KEYS.includes(currentKey) ||
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@FrederikBolding FrederikBolding Nov 5, 2025

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FORBIDDEN_KEYS already include __proto__ etc.

currentKey === '__proto__' ||
currentKey === 'constructor' ||
currentKey === 'prototype'
) {
throw rpcErrors.invalidParams(
'Invalid params: Key contains forbidden characters.',
'Invalid params: Key contains forbidden characters or is potentially prototype polluting.',
);
}

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