CVE-2021-28682 in Envoy
Summary
by MITRE • 05/21/2021
An issue was discovered in Envoy through 1.71.1. There is a remotely exploitable integer overflow in which a very large grpc-timeout value leads to unexpected timeout calculations.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 05/23/2021
The vulnerability identified as CVE-2021-28682 represents a critical integer overflow flaw within the Envoy proxy software version 1.71.1 and earlier. This issue manifests specifically within the gRPC timeout handling mechanism where the system processes extremely large timeout values that exceed the bounds of normal integer representation. The flaw exists in the core timeout calculation logic that processes gRPC request timeouts, creating a scenario where malformed or excessively large timeout values can cause arithmetic overflow conditions.
This vulnerability falls under the CWE-191 category of Integer Underflow (Wrap or Wraparound) and aligns with ATT&CK technique T1203, which involves exploiting weaknesses in timeout mechanisms to maintain persistence or gain unauthorized access. The integer overflow occurs when the system attempts to convert a very large gRPC timeout value into an internal representation that cannot accommodate such magnitude, resulting in unexpected behavior during timeout calculations. When a malicious actor submits a specially crafted gRPC request with an excessively large timeout parameter, the system's arithmetic operations overflow and produce incorrect timeout values that can be exploited for various attack vectors.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it can potentially enable attackers to manipulate timeout behaviors in ways that compromise system integrity and availability. The flaw affects the proxy's ability to accurately calculate and enforce timeout constraints, which are critical for maintaining system stability and preventing resource exhaustion attacks. When the integer overflow occurs during timeout processing, it can cause the system to either ignore timeout constraints entirely or apply incorrect timeout values that may allow attackers to prolong connections indefinitely or manipulate resource allocation patterns.
Mitigation strategies for CVE-2021-28682 should prioritize immediate patching of affected Envoy versions to 1.72.0 or later, where the integer overflow handling has been corrected. Organizations should also implement robust input validation for gRPC timeout parameters, establishing maximum value limits that prevent excessively large timeout values from being processed. Network segmentation and access controls should be strengthened to limit exposure to potentially malicious gRPC traffic, while monitoring systems should be configured to detect unusual timeout value patterns that may indicate exploitation attempts. Additionally, implementing rate limiting and connection tracking mechanisms can help prevent abuse of the timeout handling functionality and provide early detection of potential exploitation activities targeting this vulnerability.