Basis MultiDistributor — unprotected minimum-distribution list growth

Source & credit. Reproduction of a public audit finding curated by AuditVault — the original finding: 16760-setminimumdistribution-is-not-protected-trailofbits-basis-pd. Standalone Foundry PoC and full write-up: 16760-setminimumdistribution-not-protected_exp in the evm-hack-registry mirror.

Vulnerability classes: vuln/access-control/missing-auth · vuln/dos/unbounded-loop

Reproduction: local synthetic Foundry reduction; the complete passing trace is in output.txt.

Key info#

Field	Value
Loss	An arbitrary caller appends 32 entries, increasing distribution work from 1 to 33 iterations.
Vulnerable contract	`MultiDistributor.setMinimumDistribution` in test/16760-setminimumdistribution-not-protected.sol
Attacker EOA	`0x1111111111111111111111111111111111111111`
Attack contract	`Exploit`
Attack tx	Local Foundry `Exploit.run()`
Chain · block · date	Ethereum model · block 0 · synthetic
Compiler	Solidity `^0.8.24`
Bug class	Missing authorization on unbounded list mutation

TL;DR#

setMinimumDistribution is documented for trusted participants, but anyone can append token addresses. Repeated zero-minimum entries inflate every distribution loop and can eventually cause a gas-limit denial of service.

Background#

The minimum-distribution threshold exists to prevent negligible entries. It is ineffective when untrusted callers can add entries without governance or owner authorization.

The vulnerable code#

SOLIDITY

function setMinimumDistribution(address token, uint256 tokenMinDistribution) external {
    if (tokenIdx[token] == 0) tokens.push(token);
    // @> VULN: intended trusted-participant operation has no access check.
    minDistribution[token] = tokenMinDistribution;
}

Root cause#

The mutator is public and unbounded while distribute iterates the entire tokens array. No role, allowlist, or cap protects the expensive state transition.

Preconditions#

setMinimumDistribution is externally callable.
Distribution operations iterate all registered tokens.
An attacker can submit repeated transactions (or a loop in one transaction).

Attack walkthrough#

Add 32 unique token addresses with minimum distribution zero.
Invoke distribute; it loops 33 entries instead of the baseline one.
The passing trace records the enlarged loop at output.txt:4.

Diagrams#

flowchart LR A[Untrusted caller] -->|32 setter calls| L[Token list grows] L --> D[distribute loops every entry] D --> G[Gas cost / DoS pressure]

Remediation#

Restrict the setter to an owner, controller, or allowlist and cap the list length. Consider a mapping-based distribution registry or bounded iteration rather than an attacker-controlled array.

How to reproduce#

BASH

cd evm-hack-registry/16760-setminimumdistribution-not-protected_exp
forge test -vvvvv

Sources#

Reference: https://github.com/trailofbits/publications/blob/master/reviews/basis.pdf

Sources & further analysis#

Reproductions & code

Standalone PoC + full trace: 16760-setminimumdistribution-not-protected_exp (evm-hack-registry mirror).
AuditVault finding: 16760-setminimumdistribution-is-not-protected-trailofbits-basis-pd.

Alerts & third-party analyses

Web3Sec X hacked database: search.
Rekt leaderboard: search.
Solodit incident search: search.

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