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The vulnerability resides in the Elliptic Curve Integrated Encryption Scheme (ECIES) implementation used by Geth for encrypted RLPx handshakes and p2p communication . The flaw allows an attacker to extract bits of the private node key by exploiting incorrect assumptions in the cryptographic parsing logic. Specifically, when processing a specially crafted ECIES ciphertext, the `symDecrypt` function performs a slice operation `ct[:params.BlockSize]` to extract the initialization vector (IV) without first validating that the ciphertext length meets the minimum required size . The pre-decryption length check in `PrivateKey.Decrypt` was insufficient, using a `+ 1` offset rather than the required `+ params.BlockSize` to account for the IV . This allows an attacker to send a malformed ciphertext that passes validation but causes an out-of-bounds slice access during decryption . The memory access violation not only crashes the node but, through differential analysis of the resulting error states, can leak portions of the ephemeral key material used in the ECIES exchange, ultimately compromising the persistent node key. The issue was responsibly disclosed via a public pull request and affects all Geth versions prior to the patches .
DailyCVE Form:
Platform: Geth
Version: <1.16.9
Vulnerability: ECIES Key Extraction
Severity: High
date: Jan 2026
Prediction: Patch within 30 days
What Undercode Say:
Impact
Successful exploitation allows remote attackers to extract bits of the p2p node key, leading to node identity theft, man-in-the-middle attacks on the peer-to-peer network, and potential routing table poisoning. This compromises the confidentiality and integrity of all subsequent encrypted communications.
Exploit:
Minimal Proof of Concept Structure (based on public disclosure) Attacker crafts malicious ECIES ciphertext with short encrypted_message The ciphertext structure: ephemeral_pubkey(65) || encrypted_message(<16) || mac(32) Example using devp2p tool to send malicious handshake Assumes attacker has target enode address devp2p discv4 ping --addr <TARGET_NODE_IP>:30303 \ --privkey <ATTACKER_PRIVKEY> \ --payload <(python3 -c " import sys Generate valid ephemeral key and MAC, but set encrypted message to 10 bytes (<16) This triggers the out-of-bounds panic in symDecrypt sys.stdout.buffer.write(b'\x04' + b'A'64 + b'B'10 + b'C'32) Invalid ciphertext ")
Protection from this CVE
1. Upgrade Geth to patched version sudo add-apt-repository -y ppa:ethereum/ethereum sudo apt-get update sudo apt-get install ethereum -y geth version Verify v1.16.9 or v1.17.0+ 2. Rotate node key after upgrade (critical step) Stop Geth first sudo systemctl stop geth Remove existing node key to force regeneration rm -f /path/to/your/datadir/geth/nodekey Default datadir locations: ~/.ethereum/geth/nodekey /var/lib/goethereum/geth/nodekey Restart Geth - it will generate a new random node key sudo systemctl start geth 3. Verify no vulnerable peers in connection logs geth --exec 'admin.peers' attach | grep -i ecies Monitor for handshake errors indicating exploit attempts journalctl -u geth -f | grep "invalid message"
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Sources:
Reported By: github.com
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