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An attacker who transfers directly to the underlying token may control _exchangeRateStored #445

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code423n4 opened this issue May 15, 2023 · 4 comments
Closed

An attacker who transfers directly to the underlying token may control _exchangeRateStored #445

code423n4 opened this issue May 15, 2023 · 4 comments
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2 (Med Risk) Assets not at direct risk, but function/availability of the protocol could be impacted or leak value bug Something isn't working downgraded by judge Judge downgraded the risk level of this issue duplicate-220 satisfactory satisfies C4 submission criteria; eligible for awards

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Lines of code

https://github.com/code-423n4/2023-05-venus/blob/main/contracts/VToken.sol#L1476

Vulnerability details

Impact

Proof of Concept

  1. Assume that the current _totalSupply is 0 and the initial initialExchangeRateMantissa is 1:1
  2. The attacker mint 1, _totalSupply is 1, underlying.balanceOf(address(this)) is 1
  3. The attacker transfers 1 underlying token to this contract, _totalSupply is 1, underlying.balanceOf(address(this)) is 2
  4. The user expects mint 1000 and transfers 1000 underlying tokens. At this time, cashPlusBorrowsMinusReserves = 2/1 = 2, and the user gets 1000/2=500 vTokens.

Tools Used

manual

Recommended Mitigation Steps

Maintain totalCash yourself instead of using underlying.balanceOf(address(this))

Assessed type

Other
@code423n4 code423n4 added 3 (High Risk) Assets can be stolen/lost/compromised directly bug Something isn't working labels May 15, 2023
code423n4 added a commit that referenced this issue May 15, 2023
@code423n4
J4de issue #445
78ee1dd
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0xean marked the issue as duplicate of #314

@c4-judge c4-judge added duplicate-314 partial-25 Incomplete articulation of vulnerability; eligible for partial credit only (25%) labels May 17, 2023
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0xean marked the issue as partial-25

@c4-judge c4-judge added satisfactory satisfies C4 submission criteria; eligible for awards and removed partial-25 Incomplete articulation of vulnerability; eligible for partial credit only (25%) labels Jun 5, 2023
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c4-judge commented Jun 5, 2023

0xean marked the issue as satisfactory

@c4-judge c4-judge added 2 (Med Risk) Assets not at direct risk, but function/availability of the protocol could be impacted or leak value downgraded by judge Judge downgraded the risk level of this issue and removed 3 (High Risk) Assets can be stolen/lost/compromised directly labels Jun 5, 2023
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c4-judge commented Jun 5, 2023

0xean changed the severity to 2 (Med Risk)

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2 (Med Risk) Assets not at direct risk, but function/availability of the protocol could be impacted or leak value bug Something isn't working downgraded by judge Judge downgraded the risk level of this issue duplicate-220 satisfactory satisfies C4 submission criteria; eligible for awards
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