Escrow `fund()` allows issue-id griefing via front-running before the legitimate sponsor funds

Aperta
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Dal 30/9/2026.

  • #430 di @Wilfred007 — aperta

Valutazione

Difficoltà
5/5
Tempo stimato
Più di una settimana
Idoneità per principianti
15/100
Tipo di issue
Bug
Chiarezza
Specificata chiaramente
Stato di attività
Ferma
Stack tecnologico
rust
Ambito
blockchain, security

Direzione di ricerca

Start with contracts/escrow/src/lib.rs::fund() and contracts/escrow/src/test.rs, then verify Soroban transaction ordering assumptions before choosing a mitigation. Compare the funding flow with the README and consider the related patterns in the milestones and maintenance-pool contracts. Done means implementing and testing a mitigation, documenting its trust assumptions, and confirming the required test and build commands pass.

Scritto dal modello di indicizzazione a partire dal testo della issue.

Descrizione

bug GrantFox OSS Maybe Rewarded Official Campaign | FWC26 security Stellar Wave very hard

Background / Context

contracts/escrow/src/lib.rs::fund() uses issue_id (a u64 chosen off-chain by mergefi-backend/the sponsor's wallet) as the sole key into persistent storage (DataKey::Escrow(issue_id)), and rejects a second fund call on the same id with AlreadyFunded. Critically, fund performs no admin check and no validation that the caller is the "intended" sponsor for that issue — any address can call fund(issue_id, sponsor=attacker, token=<attacker-chosen>, amount=1, deadline=<attacker-chosen>) for any issue_id, as long as they supply a valid require_auth signature for themselves as sponsor.

Problem Statement

Because Stellar issue ids are presumably predictable (sequential GitHub issue numbers, or a deterministic hash the backend computes ahead of time), an attacker who front-runs the real sponsor's fund transaction — or simply calls fund proactively for issue ids they anticipate being funded — permanently claims that issue_id slot with a trivial deposit (amount=1) of a token of their choosing. The legitimate sponsor's later fund call then reverts with AlreadyFunded, and there is no top-up or re-fund-different-id path described in the README. This is a low-cost, high-impact griefing vector against a system whose entire value proposition is "sponsors fund GitHub issues."

Requirements

  • Analyze the full griefing surface: is issue_id predictable/guessable before the real fund call lands? Model the mempool/submission-ordering assumptions on Stellar/Soroban (there is no public mempool in the traditional sense, but front-running via fee/priority is still analyzed differently — investigate Soroban's actual transaction ordering guarantees).
  • Propose and implement a mitigation: options include (a) binding fund to a specific expected sponsor address set at issue-creation time by the admin/oracle, (b) a commit-reveal or admin-pre-registration step before fund is callable, (c) an admin-callable reassign/force_refund_and_reopen recovery path for squatted ids, or another design you can justify as superior.
  • Add regression tests in contracts/escrow/src/test.rs that reproduce the griefing scenario and prove the fix closes it (attacker funds first, legitimate sponsor's transaction should still succeed, or attacker's low-value funding should be recoverable without requiring off-chain intervention).
  • Document the chosen trust model change in the README's escrow section.

Acceptance Criteria

  • Written analysis of whether/why issue_id squatting is exploitable given Soroban's actual ordering model (not just Ethereum-style mempool assumptions)
  • A concrete, implemented mitigation in contracts/escrow/src/lib.rs
  • New tests proving the attack fails post-fix and existing legitimate flows (README's funding flow) still pass
  • cargo test --workspace green, make build still produces valid wasm
  • README updated to reflect the new trust assumptions for fund

Technical Notes / Hints

  • Relevant code: contracts/escrow/src/lib.rs lines ~54-88 (fund), types.rs DataKey::Escrow(u64).
  • Consider whether the fix should also apply symmetrically to create_milestone (contracts/milestones/src/lib.rs) and deposit's implicit pool-creation-on-first-deposit (contracts/maintenance-pool/src/lib.rs) — file separate issues if the fix diverges per contract, but note the shared pattern here.

Difficulty Justification

This requires understanding Soroban/Stellar's actual transaction-ordering and mempool semantics (not assumed from EVM intuition), reasoning about an economic griefing attack with no simple "add a require" fix, and designing a new access-control primitive that doesn't break the permissionless, oracle-driven trust model the rest of the contract relies on. Getting the fix wrong (e.g., adding an admin-only fund) would break the sponsor-initiated funding flow the whole product depends on.

Lingua principale
Rust
Stelle
1
Fork
102
Merge medio
4h 12m
PR unite (30g)
30

Preparare l'ambiente

  • Nessun Dockerfile né file Docker Compose
  • Ha un modello di pull request
  • Nessuna guida per i contributori

Come iniziare

  1. Leggi tutta la issue e poi la guida ai contributi del progetto.
  2. Commenta sulla issue per dire che te ne occupi tu — evita che due persone facciano lo stesso lavoro.
  3. Fai un fork del repository e lavora su un branch.
  4. Apri una pull request che faccia riferimento al numero della issue.

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