Hyperstable — RewardsDistributor.claim reverts once a ve lock expires and the reward stays in the distributor

Source & credit. Reproduction of a public audit finding curated by AuditVault — the original finding: 55694-h-03-rewarddistributorclaim-will-revert-for-tokens-with-expi. Standalone Foundry PoC and full write-up: 55694-h-03-rewarddistributorclaim-will-revert-for-tokens-with-expi_exp in the evm-hack-registry mirror.

Vulnerability classes: vuln/dos/frozen-funds · vuln/logic/incorrect-state-transition · vuln/logic/missing-check

Reproduction: Local Foundry reproduction of the verbatim claim / deposit_for pair. No fork. Trace: output.txt.

Root cause#

RewardsDistributor.claim always forwards a non-zero reward into the voting escrow with deposit_for. vePeg.deposit_for reverts when locked.end is not strictly after block.timestamp ("Cannot add to expired lock. Withdraw"). increase_unlock_time uses the same require, so the lock cannot be extended after expiry. The claim reverts and the PEG stays in the distributor.

SOLIDITY

if (amount != 0) {
    // @> VULN:
    IVotingEscrow(voting_escrow).deposit_for(_tokenId, amount);
    token_last_balance -= amount;
}

Attack path#

flowchart TD A["Two locks are funded with 1000 PEG each"] --> B["Expired lock end equals this block timestamp"] B --> C["claim loads that 1000 PEG"] C --> D["claim calls deposit_for"] D --> E["ve rejects the expired lock"] E --> F["1000 PEG remains in the distributor"] F --> G["The still-live lock claims and compounds"]

PoC#

One transaction. The expired lock's claim is a low-level call and reverts. The live lock's claim succeeds and compounds 1000 PEG into the escrow. The distributor's PEG balance is the expired 1000.

The fixed distributor pays an expired lock by transferring PEG to the owner. That control leaves the distributor at 0.

BASH

cd 55694-h-03-rewarddistributorclaim-will-revert-for-tokens-with-expi_exp
forge test -vv

Remediation#

If locked.end <= block.timestamp, transfer the reward to the lock owner instead of calling deposit_for. Hyperstable did this in commit 3012a71.

References#

AuditVault finding 55694
Report: https://github.com/solodit/solodit_content/blob/main/reports/0x52/2025-05-02-Hyperstable.md

Sources & further analysis#

Reproductions & code

Standalone PoC + full trace: 55694-h-03-rewarddistributorclaim-will-revert-for-tokens-with-expi_exp (evm-hack-registry mirror).
AuditVault finding: 55694-h-03-rewarddistributorclaim-will-revert-for-tokens-with-expi.

Alerts & third-party analyses

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Solodit incident search: search.

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