Roots — [H-01] Overwriting collateral breaks collateral gains logic

Source & credit. Reproduction of a public audit finding curated by AuditVault — the original finding: 55111-h-01-overwriting-collateral-breaks-collateral-gains-logic-pa. Standalone Foundry PoC and full write-up: 55111-h-01-overwriting-collateral-breaks-collateral-gains-logic-pa_exp in the evm-hack-registry mirror.

Vulnerability classes: integer-bounds · underflow · fix-arithmetic · known-pattern

Reproduction: self-contained Foundry PoC with only forge-std — no fork. output.txt · test/55111-…_exp.sol.

AuditVault taxonomy: lang/solidity · sector/cdp · severity/high · genome: integer-bounds · underflow · fix-arithmetic

Key info#


Impact	HIGH — reusing a sunset collateral index pays old gains in the new token; other depositors cannot claim
Protocol	Roots — `StabilityPool` collateral enable / gains
Vulnerable code	Overwrite clears `epochToScaleToSums` but not `collateralGainsByDepositor` / `depositSums`
Bug class	Incomplete state wipe on index reuse
Finding	Pashov Audit Group — Roots security review 2025-02-09 · #55111
Report	Roots-security-review_2025-02-09.md
Source	AuditVault
Fix	Do not overwrite sunset collaterals; add disable-after-expiry without reusing dirty indices
Compiler	`^0.8.24` (PoC)

TL;DR#

Alice accrues coll-A gains on stability-pool index 0 and leaves them unclaimed.
Coll A is sunset; coll C is enabled and reuses index 0.
Product sums for index 0 are zeroed; Alice's pending gain mapping is not.
Alice claims index 0 and is paid in coll-C tokens for her coll-A leftover, draining the pool.
Bob's coll-C claim reverts (transfer amount exceeds balance).

Vulnerable code#

SOLIDITY

function _overwriteCollateral(uint256 index, MockCollateral coll) internal {
    collateralTokens[index] = coll;
    sunsetExpiry[index] = 0;
    epochToScaleToSums[index][0][0] = 0; // @> VULN: only product sums cleared
    // depositSums[*][index] and collateralGainsByDepositor[*][index] left dirty
}

Fix: never reuse sunset indices, or wipe all per-depositor gain state for the index before reuse.

Diagrams#

sequenceDiagram participant Alice participant Bob participant SP as StabilityPool participant CA as CollA participant CC as CollC Alice->>SP: provide + accrue collA gains 50 Note over SP: index0 gains Alice=50 SP->>SP: sunset collA then enable collC at index0 SP->>SP: clear product sums only SP->>CC: mint 50 into pool Alice->>SP: claimCollateralGains index0 SP->>Alice: transfer 50 collC via leftover collA gain Bob->>SP: claim collC SP-->>Bob: revert empty pool

Impact#

Depositors of a new collateral can have their gains drained by leftover accounting from a previous collateral on the same index; claims may also DoS via underflow on sums - depSums.

Sources#

AuditVault #55111
Pashov Roots 2025-02-09
Reduced StabilityPool overwrite path from the finding (sunset expiry reduced to immediate for offline PoC)

Sources & further analysis#

Reproductions & code

Standalone PoC + full trace: 55111-h-01-overwriting-collateral-breaks-collateral-gains-logic-pa_exp (evm-hack-registry mirror).
AuditVault finding: 55111-h-01-overwriting-collateral-breaks-collateral-gains-logic-pa.

Alerts & third-party analyses

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