SXT — [C-01] Accepting duplicate signatures from one signer

Source & credit. Reproduction of a public audit finding curated by AuditVault — the original finding: 63314-c-01-accepting-duplicate-signatures-from-one-signer-pashov-a. Standalone Foundry PoC and full write-up: 63314-c-01-accepting-duplicate-signatures-from-one-signer-pashov-a_exp in the evm-hack-registry mirror.

Vulnerability classes: broken-logic · role-bypass · bridge-validator-threshold

Reproduction: self-contained Foundry PoC, forge-std only.

AuditVault taxonomy: severity/high · sector/staking · platform/pashov · broken-logic · role-bypass · bridge-validator-threshold

Key info#


Impact	HIGH — single attestor meets multi-sig threshold via replayed signature
Protocol	SXT SubstrateSignatureValidator
Vulnerable code	`validateMessage` increments count without signer dedup
Bug class	Missing signature uniqueness check
Finding	Pashov · SXT 2025-03-31 · #63314

TL;DR#

Threshold = 2. Attacker submits the same valid (v,r,s) twice. Both recover to one attestor; both count. validateMessage returns true.

The vulnerable code#

SOLIDITY

if (attestorIndex < attestorsLength && _attestors[attestorIndex] == recoveredAddress) {
    ++validSignaturesCount; // @> VULN no dedup
}
// FIX: skip if signer already counted

Diagrams#

flowchart LR S1["sig of attestor A"] --> V["validateMessage"] S1b["same sig again"] --> V V --> T["validCount equals 2"] T --> OK["threshold met"]

Impact#

Forged multi-attestor consensus from one honest signature → bridge/message validation bypass.

Sources#

Sources & further analysis#

Reproductions & code

Standalone PoC + full trace: 63314-c-01-accepting-duplicate-signatures-from-one-signer-pashov-a_exp (evm-hack-registry mirror).
AuditVault finding: 63314-c-01-accepting-duplicate-signatures-from-one-signer-pashov-a.

Alerts & third-party analyses

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Solodit incident search: search.

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