CVE-2020-35471 in Envoy
Summary
by MITRE • 12/15/2020
Envoy before 1.16.1 mishandles dropped and truncated datagrams, as demonstrated by a segmentation fault for a UDP packet size larger than 1500.
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Analysis
by VulDB Data Team • 12/18/2020
The vulnerability identified as CVE-2020-35471 affects the Envoy proxy software version 1.16.1 and earlier, representing a critical flaw in how the system processes UDP datagrams that exceed the standard maximum transmission unit size of 1500 bytes. This issue manifests when Envoy encounters UDP packets that are larger than the expected size limits, leading to improper handling of dropped or truncated datagrams during packet processing. The flaw specifically impacts the proxy's ability to manage network traffic efficiently when dealing with oversized packets, creating a potential pathway for system instability and service disruption.
The technical root cause of this vulnerability stems from inadequate validation and handling mechanisms within Envoy's UDP packet processing pipeline. When a UDP packet exceeds 1500 bytes, the proxy fails to properly manage the truncation or dropping of these oversized datagrams, resulting in a segmentation fault that crashes the process. This behavior aligns with CWE-121, which addresses stack-based buffer overflow conditions, and CWE-122, which covers heap-based buffer overflow scenarios. The flaw demonstrates a classic memory safety issue where the software does not properly account for boundary conditions when processing network packets, particularly those that exceed standard size constraints.
The operational impact of this vulnerability extends beyond simple service interruption to potentially enable denial of service attacks against systems relying on Envoy as their network proxy. Attackers could exploit this weakness by sending oversized UDP packets to target services, causing the proxy to crash and restart, thereby disrupting network connectivity for legitimate users. This vulnerability particularly affects environments where Envoy is deployed as a sidecar proxy in service mesh architectures or as a standalone load balancer, where continuous availability is critical. The segmentation fault represents a complete system failure condition that would require manual intervention to restore service, creating significant operational overhead for security teams managing these deployments.
Mitigation strategies for CVE-2020-35471 primarily involve upgrading to Envoy version 1.16.1 or later, which includes patches addressing the improper handling of oversized UDP packets. Organizations should also implement network-level controls such as ingress filtering to drop oversized UDP packets before they reach the proxy, and consider implementing rate limiting to prevent abuse of the vulnerability. Security monitoring should be enhanced to detect unusual patterns of proxy crashes or restarts that might indicate exploitation attempts. Additionally, implementing proper input validation and boundary checking mechanisms within the proxy configuration can help reduce the attack surface. The vulnerability also highlights the importance of adhering to ATT&CK framework principles for network defense, particularly in the context of command and control operations where such proxy vulnerabilities could be leveraged for lateral movement within compromised networks. Organizations should conduct thorough testing of updated versions to ensure compatibility with existing configurations while maintaining robust network security postures that include regular vulnerability assessments and penetration testing to identify similar weaknesses in their infrastructure.