CVE-2020-8806
📋 TL;DR
This vulnerability in Zcashd allows attackers to create alternative blockchain branches that could be incorrectly accepted, potentially enabling double-spending attacks. It affects Zcash cryptocurrency nodes running vulnerable versions, allowing malicious actors to disrupt consensus and manipulate transactions.
💻 Affected Systems
- Electric Coin Company Zcashd
📦 What is this software?
Zcashd by Electriccoin
⚠️ Risk & Real-World Impact
Worst Case
Complete consensus failure across the Zcash network enabling widespread double spending, devaluation of cryptocurrency, and loss of funds for exchanges and users.
Likely Case
Targeted double-spending attacks against specific transactions, causing financial losses for merchants and exchanges accepting Zcash payments.
If Mitigated
No impact if patched; unpatched nodes risk being on forked chains with potential transaction reversals.
🎯 Exploit Status
Exploitation requires blockchain manipulation capabilities but no authentication to vulnerable nodes.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.1.1-1 and later
Vendor Advisory: https://electriccoin.co/blog/new-releases-2-1-1-and-hotfix-2-1-1-1/
Restart Required: Yes
Instructions:
1. Stop Zcashd service. 2. Backup wallet.dat and zcash.conf. 3. Download and install Zcashd 2.1.1-1 or later from official sources. 4. Restart Zcashd service. 5. Verify blockchain synchronization.
🔧 Temporary Workarounds
Temporary Node Shutdown
allShut down vulnerable Zcashd nodes until patched to prevent exploitation
sudo systemctl stop zcashd
zcash-cli stop
🧯 If You Can't Patch
- Disable Zcashd service completely until patching is possible
- Monitor blockchain for unusual forks or double-spend attempts
🔍 How to Verify
Check if Vulnerable:
Check Zcashd version with 'zcashd --version' and compare to vulnerable rangeCheck Version:
zcashd --version | grep versionVerify Fix Applied:
Verify version is 2.1.1-1 or later and monitor for consensus issues📡 Detection & Monitoring
Log Indicators:
- Block validation errors
- Consensus failure messages
- Unexpected chain reorganizations
Network Indicators:
- Unusual blockchain forks
- Multiple valid chains appearing
SIEM Query:
source="zcashd.log" AND ("consensus" OR "validation" OR "reorg") AND ("error" OR "fail" OR "invalid")