CVE-2020-26264 in Go Ethereum
Summary
by MITRE • 12/11/2020
Go Ethereum, or "Geth", is the official Golang implementation of the Ethereum protocol. In Geth before version 1.9.25 a denial-of-service vulnerability can make a LES server crash via malicious GetProofsV2 request from a connected LES client. This vulnerability only concerns users explicitly enabling les server; disabling les prevents the exploit. The vulnerability was patched in version 1.9.25.
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Analysis
by VulDB Data Team • 12/16/2020
The vulnerability identified as CVE-2020-26264 represents a critical denial-of-service weakness within the Go Ethereum client implementation known as Geth. This issue specifically targets the Light Ethereum Subprotocol (LES) server functionality that enables lightweight clients to communicate with full nodes. The vulnerability exists in versions prior to 1.9.25 and demonstrates how improperly validated client requests can lead to complete service disruption. The flaw manifests when a malicious LES client sends a specially crafted GetProofsV2 request to a vulnerable LES server, causing the server to crash and become unavailable to legitimate clients. This vulnerability is particularly concerning because it requires no authentication or elevated privileges to exploit, making it accessible to any connected client that can establish a connection to the vulnerable server. The issue is classified under CWE-400 as an uncontrolled resource consumption vulnerability, where the server's resources become exhausted through malformed input processing. From an operational perspective, this vulnerability directly impacts the availability and reliability of Ethereum network infrastructure, as it can be leveraged to disrupt access to blockchain data and services. The attack vector aligns with ATT&CK technique T1499.004 for network denial-of-service, specifically targeting the availability component of the CIA triad.
The technical implementation of this vulnerability stems from inadequate input validation within the GetProofsV2 request processing mechanism in the LES server component. When a malicious client submits a malformed request containing excessive or malformed data elements, the server's processing logic fails to properly handle the edge cases, leading to memory corruption or stack overflow conditions. The vulnerability is specifically tied to the way the LES server handles proof data structures and their associated metadata during the proof verification process. The server's failure to implement proper bounds checking and input sanitization allows attackers to craft requests that trigger unexpected behavior in the underlying data structures. This processing failure causes the server to enter an unrecoverable state, resulting in a complete crash and service termination. The vulnerability's exploitation requires only a single malicious request, making it particularly dangerous as it can be executed repeatedly to maintain service disruption. The fix implemented in version 1.9.25 addresses this by introducing proper input validation, implementing stricter bounds checking, and adding defensive programming measures to prevent the server from crashing under malformed input conditions.
The operational impact of CVE-2020-26264 extends beyond simple service disruption to potentially compromise the broader Ethereum network's reliability and trustworthiness. Network operators who have LES functionality enabled face significant risk of being targeted by malicious actors seeking to disrupt their services or gain competitive advantages through service degradation. The vulnerability affects any Ethereum node operator who explicitly enables the LES server functionality, which is commonly used in resource-constrained environments or for specific network optimization purposes. Organizations relying on Geth for their Ethereum infrastructure must carefully evaluate their deployment configurations and ensure that LES servers are either properly secured or disabled when not required. The vulnerability also highlights the importance of regular security updates and patch management processes within blockchain infrastructure. From a security posture perspective, this vulnerability demonstrates how even minor protocol implementations can introduce significant risks when proper input validation and error handling mechanisms are not implemented. The attack scenario represents a classic example of how insufficient defensive programming can lead to catastrophic service failures, particularly in distributed systems where availability is paramount for network health. Network monitoring and intrusion detection systems should be configured to identify unusual patterns in LES server traffic that might indicate attempted exploitation of this vulnerability. The remediation process requires careful deployment of the patched version 1.9.25 or later, with proper testing to ensure that legitimate network operations continue unaffected while the vulnerability is addressed.