Strata Tranches — sUSDe withdrawers always incur a loss (inverted CDO params)

Source & credit. Reproduction of a public audit finding curated by AuditVault — the original finding: 63222-withdrawers-of-susde-always-incur-a-loss-because-parameters. Standalone Foundry PoC and full write-up: 63222-withdrawers-of-susde-always-incur-a-loss-because-parameters_exp in the evm-hack-registry mirror.

Vulnerability classes: wrong-order · indirect-loss · parameter-swap

Reproduction: self-contained Foundry PoC, forge-std only, no fork. Full trace: output.txt.

AuditVault taxonomy: severity/high · sector/oracle · sector/staking · platform/cyfrin · wrong-order · indirect-loss

Key info#


Impact	HIGH — withdrawer burns full Tranche shares but receives ~66% of requested sUSDe
Protocol	Strata Tranches v2.0
Vulnerable code	`Tranche::_withdraw` → `cdo.withdraw(..., baseAssets, tokenAssets)` inverted
Bug class	Swapped call arguments
Finding	Cyfrin · Strata 2025-10-08 · #63222
Report	Cyfrin Strata
Compiler	`^0.8.24`

TL;DR#

Withdraw of 100 sUSDe (worth 150 USDe at 1.5 rate) burns 150 JRT shares.
Tranche passes (baseAssets, tokenAssets) but CDO expects (tokenAmount, baseAssets).
Strategy runs previewWithdraw(tokenAssets) instead of previewWithdraw(baseAssets) → ~66.67 sUSDe out.
User permanently loses USDe value relative to burned shares.

The vulnerable code#

SOLIDITY

cdo.withdraw(address(this), token, baseAssets, tokenAssets, receiver); // @> VULN inverted
// FIX: cdo.withdraw(address(this), token, tokenAssets, baseAssets, receiver);

Root cause#

Argument order mismatch between Tranche and CDO/Strategy withdraw APIs.

Preconditions#

sUSDe/USDe exchange rate ≠ 1 (after yield).
User withdraws sUSDe (not plain USDe).

Attack walkthrough#

Bootstrap sUSDe rate to 1.5 via yield donation.
Deposit 100 sUSDe → 150 JRT.
Withdraw 100 sUSDe → all shares burned, ~66.67 sUSDe returned.

Diagrams#

sequenceDiagram participant User participant Tranche participant CDO participant Strategy User->>Tranche: withdraw 100 sUSDe Tranche->>Tranche: burn 150 JRT Tranche->>CDO: withdraw baseAssets then tokenAssets Note over CDO: args inverted CDO->>Strategy: previewWithdraw wrong base Strategy-->>User: ~66.67 sUSDe

Impact#

Every sUSDe withdrawal under-pays the user while burning full share entitlement.

Sources#

AuditVault #63222
Cyfrin Strata Tranches v2.0
Fixed: Strata-Money/contracts-tranches@31d9b72

Sources & further analysis#

Reproductions & code

Standalone PoC + full trace: 63222-withdrawers-of-susde-always-incur-a-loss-because-parameters_exp (evm-hack-registry mirror).
AuditVault finding: 63222-withdrawers-of-susde-always-incur-a-loss-because-parameters.

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