Suzaku: Reward distribution divides by a zero historical-epoch stake, bricking the epoch forever

Source & credit. Reproduction of a public audit finding curated by AuditVault — the original finding: 61239-division-by-zero-in-rewards-distribution-can-cause-permanent. The historical source/toolchain is unavailable; this entry is documentation only and claims no executable Forge PoC.

Vulnerability classes: vuln/division-by-zero · vuln/permanent-dos · vuln/reward-accounting

Reproduction: a faithful minimal reproduction of the vulnerable finding — the vulnerable function is reproduced verbatim (marked @>) with faithful minimal doubles; local deploy, no fork.

Root cause#

distribution fetches the CURRENT asset classes but reads the PAST epoch's totalStakeCache, which is 0 for an asset class that had no stake in that epoch. Math.mulDiv(operatorStake, BASIS_POINTS_DENOMINATOR, totalStake) (line 147) then divides by zero and reverts — permanently bricking that epoch's reward distribution.

SOLIDITY

            uint16 assetClassShare = rewardsSharePerAssetClass[assetClasses[i]];

            uint256 shareForClass = Math.mulDiv(
                Math.mulDiv(operatorStake, BASIS_POINTS_DENOMINATOR, totalStake), // @> DIVISION BY ZERO: totalStake == 0 for historical epoch
                assetClassShare,

Why it's exploitable here#

The code fetches the CURRENT asset classes but the HISTORICAL epoch's stake, which can be 0 for a class that did not exist/stake then.
mulDiv(_, _, totalStake) with totalStake == 0 reverts on division by zero.
The revert is deterministic and unavoidable, so the epoch's rewards can never be distributed.

Attack path#

flowchart TD A["Distribute rewards for a historical epoch"] --> B["Fetch CURRENT asset classes"] B --> C["Read PAST epoch totalStakeCache == 0"] C --> D["mulDiv(operatorStake, BP, totalStake=0)"] D --> E["Division by zero → revert"] E --> F["Epoch's 1,000 ETH rewards permanently bricked"]

Marked-line walkthrough (Playground)#

The EVM Playground pins each step to the exact executed source line in Rewards:

Line 140 — getAssetClassIds() returns the classes that exist NOW, not those staked in the historical epoch.
Line 143 — VULN. totalStakeCache(epoch, class) is 0 for a class with no stake that epoch; the next line's mulDiv(operatorStake, BP, totalStake) (147) divides by zero and reverts forever, blocking the epoch's 1,000 ETH rewards.

PoC#

Registry (Foundry, local deploy — exploit path + a fixed-variant control):

BASH

cd 61239-division-by-zero-in-rewards-distribution-can-cause-permane_exp
forge test -vv

Expected: both tests PASS — the exploit test distributes an epoch with a zero-stake class and asserts the 1,000-ETH pool is permanently blocked; the fixed guard skips the class and distributes normally. The browser EVM Playground is served at /hacks/61239-division-by-zero-in-rewards-distribution-can-cause-permane/.

Remediation#

Guard totalStake == 0 (skip the class or contribute a zero share) before the mulDiv division.

References#

AuditVault finding: https://github.com/Auditware/AuditVault/blob/main/findings/61239-division-by-zero-in-rewards-distribution-can-cause-permanent.md

Sources & further analysis#

Reproductions & code

No executable Forge reproduction is claimed; the historical source/toolchain was unavailable for this finding.
AuditVault finding: 61239-division-by-zero-in-rewards-distribution-can-cause-permanent.
Upstream DeFiHackLabs PoC directory: src/test.

Alerts & third-party analyses

DeFiHackLabs incident explorer: search "Suzaku: Reward distribution divides by a zero historical-epoch stake, bricking the epoch forever".
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