KittenSwap — Lack of `lastMintedPeriod` update allows unlimited minting of Kitten

Source & credit. Reproduction of a public audit finding curated by AuditVault — the original finding: 58066-c-02-lack-of-lastmintedperiod-update-allows-unlimited-mintin. Standalone Foundry PoC and full write-up: 58066-c-02-lack-of-lastmintedperiod-update-allows-unlimited-mintin_exp in the evm-hack-registry mirror.

Vulnerability classes: access-roles · specific-token-type · inflation

Reproduction: self-contained Foundry PoC with only forge-std — no fork. output.txt · test/58066-…sol.

AuditVault taxonomy: lang/solidity · sector/farm · sector/token · severity/high · genome: access-roles · specific-token-type

Key info#


Impact	HIGH — Kitten emissions mint unbounded once the first period elapses
Protocol	KittenSwap — `Minter.updatePeriod`
Vulnerable code	`if (currentPeriod > lastMintedPeriod)` never followed by `lastMintedPeriod = currentPeriod`
Bug class	Missing state update / emission guard bypass
Finding	Pashov Audit Group — KittenSwap 2025-06-12 · #58066
Report	KittenSwap-security-review_2025-06-12.md
Source	AuditVault
Fix	`lastMintedPeriod = currentPeriod` after the mint
Compiler	`^0.8.24` (PoC)

TL;DR#

Minter.updatePeriod() is meant to mint weekly Kitten once per epoch period.
The guard is if (currentPeriod > lastMintedPeriod).
After minting, the code never writes lastMintedPeriod = currentPeriod.
Once period advances past the initial value, every call remints the full weekly amount.

Vulnerable code#

SOLIDITY

if (currentPeriod > lastMintedPeriod) { // @> VULN
    // mint emissions to rebaseReward + voter
    // FIX: lastMintedPeriod = currentPeriod;
    return true;
}

Root cause#

A one-sided guard: the comparison is present, but the state variable that makes it one-shot is never updated. After the first successful period, lastMintedPeriod stays at 0 forever.

Preconditions#

At least one period has elapsed so currentPeriod > lastMintedPeriod (initially 1 > 0).
Caller can invoke updatePeriod (permissionless in the audited design).

Attack walkthrough#

First updatePeriod() mints 1× weekly (legitimate).
Nine more calls each remint another weekly amount.
Supply = 10× weekly; lastMintedPeriod still 0.

Diagrams#

sequenceDiagram participant Anyone participant Minter participant Kitten Note over Minter: lastMintedPeriod = 0, currentPeriod = 1 Anyone->>Minter: updatePeriod() Minter->>Kitten: mint weekly Note over Minter: lastMintedPeriod still 0 Anyone->>Minter: updatePeriod() x9 Minter->>Kitten: mint weekly x9 Note over Kitten: supply = 10x weekly

Impact#

Unbounded Kitten inflation dilutes all holders and corrupts emissions to RebaseReward / Voter.

Sources#

AuditVault #58066
Pashov KittenSwap 2025-06-12
Reduced from Kittenswap/contracts review commit 65c8bdd (private at time of reduction; logic from report + Solidly-style minter)

Sources & further analysis#

Reproductions & code

Standalone PoC + full trace: 58066-c-02-lack-of-lastmintedperiod-update-allows-unlimited-mintin_exp (evm-hack-registry mirror).
AuditVault finding: 58066-c-02-lack-of-lastmintedperiod-update-allows-unlimited-mintin.

Alerts & third-party analyses

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Solodit incident search: search.

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