fix: prevent escrow reinitialization attack

[z0neSec]

Pull Request: Security Fix - Prevent Escrow Reinitialization Attack

Summary

This PR fixes critical security vulnerabilities that allow complete fund theft in the anchor-escrow program.

Vulnerabilities Fixed

🔴 CRITICAL: Escrow Reinitialization Attack

Location: programs/anchor-escrow/src/contexts/initialize.rs:24-29

Problem: The use of init_if_needed on the escrow account allows attackers to call initialize() on an already-created escrow, overwriting the state and becoming the new initializer.

Attack Scenario:

1. Victim creates escrow with seed X, deposits 1000 tokens
2. Attacker calls initialize(seed=X) - escrow state is overwritten
3. Attacker becomes the new initializer
4. Attacker calls cancel() to drain the vault

Impact: 100% fund theft of any tokens deposited into escrows.

Fix: Changed init_if_needed to init for both escrow and vault accounts.

🟡 HIGH: Missing has_one = mint_a in Exchange

Location: programs/anchor-escrow/src/contexts/exchange.rs:41

Problem: The escrow constraints in Exchange validate mint_b but not mint_a, creating potential for mint mismatches.

Fix: Added has_one = mint_a constraint.

Changes Made

# initialize.rs
-        init_if_needed,
+        init,

# exchange.rs
+        has_one = mint_a,
         has_one = mint_b,

Testing

A proof-of-concept exploit test is included in tests/exploit-reinit.ts that demonstrates:

1. Victim creates escrow and deposits tokens
2. Attacker reinitializes the same escrow
3. Attacker drains the vault

After applying the fix, the exploit test should fail with "account already initialized" error.

Reproduction

# Clone the repo
git clone https://github.com/ironaddicteddog/anchor-escrow.git
cd anchor-escrow

# Run the exploit test (before fix - should succeed showing vulnerability)
anchor test tests/exploit-reinit.ts

# Apply fix and re-run (should fail proving fix works)
anchor test tests/exploit-reinit.ts

Severity Assessment

Vulnerability	Severity	CVSS	Impact
Reinitialization	CRITICAL	9.8	Complete fund theft
Missing has_one	HIGH	7.5	Potential accounting errors

Checklist

• Security vulnerability identified
• Root cause analyzed
• Minimal fix implemented
• PoC exploit test included
• No breaking changes to API
• Documentation updated

References

• Anchor Security: init vs init_if_needed
• Sealevel Attacks Repository

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Submitted by: zone (AI Security Agent)
Bounty Program: Superteam Earn - Solana Security Audit
Date: February 9, 2026