Mute.Io — Bond max-buyer might end up buying the max buy of the next epoch

Source & credit. Reproduction of a public audit finding curated by AuditVault — the original finding: 16038-h-01-bond-max-buyer-might-end-up-buying-the-max-buy-of-the-n. Standalone Foundry PoC and full write-up: 16038-h-01-bond-max-buyer-might-end-up-buying-the-max-buy-of-the-n_exp in the evm-hack-registry mirror.

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

AuditVault taxonomy: lang/solidity · platform/code4rena · severity/high · sector/dex · genome: wrong-condition · direct-drain

Key info#


Impact	HIGH — max_buy after epoch flip purchases full next-epoch allocation at worse price
Protocol	Mute.Io
Bug class	`max_buy` uses live `maxPurchaseAmount()` with no epoch pin
Finding	Code4rena 2023-03-mute H-01 · #16038
Report	https://code4rena.com/reports/2023-03-mute
Source	AuditVault
Status	Audit finding — reproduced as a standalone local synthetic
Compiler	`^0.8.24` (PoC)

TL;DR#

deposit(..., max_buy=true) ignores the caller's intended epoch and always takes the current epoch's remaining max. If the epoch rolls before inclusion, the buyer silently purchases the entire next epoch.

HARM: victim intended 1 wad remainder, received full 100 wad next-epoch max payout.

Root cause#

No epoch-id check on the max_buy path.

Preconditions#

Near-exhausted epoch; concurrent fill or frontrun rolls epoch before victim's max_buy lands.

Attack walkthrough#

Seed 99% filled → attacker max_buy exhausts remainder → victim max_buy takes full next epoch.

Diagrams#

flowchart TD A["Epoch 0: 1 wad left"] --> B["Victim intends max_buy of 1"] A --> C["Attacker max_buy exhausts epoch"] C --> D["Epoch 1 starts full"] B --> E["Victim max_buy lands"] D --> E E --> F["Buys full 100 wad next epoch"]

Impact#

Users over-purchase bonds at worse pricing than intended when epochs roll mid-flight.

Sources#

AuditVault finding
Report: https://code4rena.com/reports/2023-03-mute
Reduced source provenance: github.com/code-423n4/2023-03-mute@4d8b13a contracts/bonds/MuteBond.sol

Sources & further analysis#

Reproductions & code

Standalone PoC + full trace: 16038-h-01-bond-max-buyer-might-end-up-buying-the-max-buy-of-the-n_exp (evm-hack-registry mirror).
AuditVault finding: 16038-h-01-bond-max-buyer-might-end-up-buying-the-max-buy-of-the-n.

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.

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