FunctionToString overflows on cyclic Proxy prototype chains

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Ninguém assumiu esta issue ainda.

  • #25964 de @chiliec — fechado sem integrar

Avaliação

Dificuldade
4/5
Tempo estimado
3-5 dias
Facilidade para iniciantes
35/100
Tipo de issue
Bug
Clareza
Razoavelmente clara
Status de atividade
Estagnada
Stack de tecnologia
javascript, typescript
Domínio
devtools

Direção de pesquisa

Start with functionToStringIntegration and packages/core/src/utils/object.ts, focusing on how getOriginalFunction reads __sentry_original__. Use the reproduction in the issue to investigate the cyclic Proxy case; done means the wrapped toString returns normally for that case without changing native behavior.

Escrita pelo modelo de indexação a partir do texto da issue.

Descrição

Browser Bug

The patched Function.prototype.toString from functionToStringIntegration throws RangeError: Maximum call stack size exceeded for a function whose prototype chain loops back through a Proxy. Native toString returns normally for the same function. Anti-tamper and fingerprinting scripts use this kind of probe to detect patched natives.

Reported by Sergio Lombana from a customer on @sentry/[email protected] with Castle bot detection loaded. Their event has a short stack: the Sentry toString wrapper is the top frame and the frames below it are Castle's.

Root cause (high confidence for the repro, unverified for the customer's exact trigger)

The wrapper calls getOriginalFunction(this), which reads this.__sentry_original__ (packages/core/src/utils/object.ts). For a function without that own property, the read walks the prototype chain. If the chain loops back through a Proxy, the walk never ends and overflows inside the wrapper frame. Native toString never reads properties from this, so it doesn't overflow.

This still happens on develop after #25921 / #25922. Those PRs fixed the apply re-entry and huge-argument-list overflows, not this property lookup.

Reproduction

const orig = Function.prototype.toString;
const callOrig = Function.prototype.call.bind(orig);

function f() {}
Object.setPrototypeOf(f, Object.create(new Proxy(f, {})));

Function.prototype.toString.call(f); // native: 'function f() {}'

// same shape as the current wrapper on develop
Function.prototype.toString = function () {
  const o = this.__sentry_original__;
  return callOrig(o ?? this);
};

Function.prototype.toString.call(f); // RangeError: Maximum call stack size exceeded

Unknowns

  • Someone else reproduced this artificial case but couldn't trigger the error with the same Castle and SDK versions. So it's not confirmed that this is the probe Castle runs in the customer's environment.

Workaround

  • Filter the RangeError via ignoreErrors / beforeSend. Removing functionToStringIntegration can make Sentry-wrapped functions look tampered to anti-bot scripts, so it isn't recommended here.

Related: #21965, #22515, #25921, #25922

via Sergio.

--

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