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Reproduced Exploit

Stake.Link reSDL bridge — stale approval steals returned lock

handleOutgoingRESDL removes the lock owner but does not delete its transfer approval. When the same ID returns to a victim, the stale approved account transfers the lock away.

Dec 2023•Other•access-control•1 min read

Chain

Other

Category

access-control

Date

Dec 2023

Source

AuditVault

PoC & write-upPoC for your local evm-hack-analyzerAuditVault PoCs

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Source & credit. Reproduction of a public audit finding curated by AuditVault — the original finding: 29738-a-user-can-steal-an-already-transfered-and-bridged-resdl-loc. Standalone Foundry PoC and full write-up: 29738-a-user-can-steal-an-already-transfered-and-bridged-resdl-loc_exp in the evm-hack-registry mirror.

Vulnerability classes: vuln/access-control/missing-check · vuln/bridge/missing-validation

Key info#

FieldValue
LossBridged reSDL lock is stolen from its recipient
ChainLocal synthetic

TL;DR#

handleOutgoingRESDL removes the lock owner but does not delete its transfer approval. When the same ID returns to a victim, the stale approved account transfers the lock away.

The vulnerable code#

SOLIDITY
delete ownerOf[id]; /* FIX: delete tokenApprovals[id]; */ // @> VULN: bridge departure deletes owner but preserves stale transfer approval.

Attack walkthrough#

The seller pre-approves an alternate account, bridges the lock to a victim, and the alternate account calls transferFrom after the lock returns. The local PoC asserts that the attacker is final owner.

Diagrams#

sequenceDiagram participant S as Seller participant B as Bridge pool participant V as Victim S->>B: set stale approval and bridge lock B-->>V: return same lock ID S->>B: approved alternate transfers lock

Remediation#

Delete tokenApprovals[lockId] when outgoing bridging burns or removes lock ownership.

Sources#

Sources & further analysis#

Reproductions & code

Alerts & third-party analyses

  • Web3Sec X hacked database: search.
  • Rekt leaderboard: search.
  • Solodit incident search: search.

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