Folks Finance mixes stable and variable debt — AuditVault 61091

Source & credit. Reproduction of a public audit finding curated by AuditVault — the original finding: 61091. Standalone Foundry PoC and full write-up: 61091-folks-liquidation-mixing_exp in the evm-hack-registry mirror.

Vulnerability classes: vuln/logic/liquidation-logic · vuln/logic/incorrect-state-transition

Reproduction: Fully local synthetic reduction. Run forge test -vvv in this folder; no live RPC is required.

Key info#

Field	Value
Protocol	Audit finding 61091
Impact	High
Loss	Reduced invariant reproduced; no live funds moved
Attacker EOA	Configured synthetic caller
Attack contract	`Exploit`
Attack tx	Local Foundry `Exploit.attack()` call
Chain · block · date	Ethereum model · block 1 · synthetic
Bug class	See vulnerability-class tags above
Vulnerable contract	`Vulnerable` in `test/61091-folks-liquidation-mixing.sol`
Attack contract	`Exploit`
Compiler	Solidity 0.8.24
Reproduction	Local reduced model

TL;DR#

Liquidation merges stable debt into the variable bucket, changing the borrower’s debt semantics.

Background#

The report identifies a state/accounting boundary that can be reached by an untrusted caller. This self-contained model keeps the relevant variables and call ordering while removing unrelated protocol dependencies.

The vulnerable code#

The minimized victim and attack contracts are in test/61091-folks-liquidation-mixing.sol. The marked operation is executed by Exploit.attack() and asserted by the Foundry test.

Root cause#

The vulnerable operation omits the validation or state update required by the report, so the resulting state no longer matches the intended invariant.

Preconditions#

The affected entry point is deployed and reachable; no privileged role is needed in this reduced reproduction.

Attack walkthrough#

Deploy the reduced victim from Exploit.
Execute the reported call sequence.
Assert the resulting state mismatch in test_exploit.

Diagrams#

flowchart TD A[Attacker] --> B[Vulnerable entry point] B --> C[Missing check or state update] C --> D[Incorrect state / denial of service]

Remediation#

Validate caller-controlled inputs and perform the accounting/state transition atomically before any external effect. Add a regression test for the reported invariant.

How to reproduce#

BASH

forge test -vvv

Sources#

AuditVault finding: https://github.com/Auditware/AuditVault/blob/main/findings/61091.md
Original report: https://github.com/immunefi-team/Past-Audit-Competitions/blob/main/Folks%20Finance/Boost%20_%20Folks%20Finance%2034190%20-%20%5BSmart%20Contract%20-%20Critical%5D%20Liquidated%20users%20can%20mix%20and%20manipulate%20stable%20and%20variable%20borrowings%20through%20exploitative%20liquidation%20process.md
Synthetic reduction: test/61091-folks-liquidation-mixing.sol (local reduction)

Reference: AuditVault finding 61091

Sources & further analysis#

Reproductions & code

Standalone PoC + full trace: 61091-folks-liquidation-mixing_exp (evm-hack-registry mirror).
AuditVault finding: 61091.

Alerts & third-party analyses

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

These dashboards index community alerts tweets, post-mortems, and independent write-ups. Reach them through the protocol name above to cross-check this reproduction against other analyses.

Source-level debugger — step opcodes and Solidity in sync