CVE-2023-45288 in net-http
Summary
by MITRE • 04/05/2024
An attacker may cause an HTTP/2 endpoint to read arbitrary amounts of header data by sending an excessive number of CONTINUATION frames. Maintaining HPACK state requires parsing and processing all HEADERS and CONTINUATION frames on a connection. When a request's headers exceed MaxHeaderBytes, no memory is allocated to store the excess headers, but they are still parsed. This permits an attacker to cause an HTTP/2 endpoint to read arbitrary amounts of header data, all associated with a request which is going to be rejected. These headers can include Huffman-encoded data which is significantly more expensive for the receiver to decode than for an attacker to send. The fix sets a limit on the amount of excess header frames we will process before closing a connection.
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Analysis
by VulDB Data Team • 07/27/2025
The vulnerability described in CVE-2023-45288 represents a significant denial of service weakness in HTTP/2 implementations that stems from improper handling of header frame processing. This flaw allows attackers to exploit the HPACK compression state management mechanism by flooding connections with excessive CONTINUATION frames, effectively causing resource exhaustion without necessarily consuming excessive memory. The vulnerability specifically targets the parsing logic that manages header data in HTTP/2 connections, where the system continues to process header frames even when the total header size exceeds the configured maximum limit. This behavior creates a scenario where computational resources are consumed unnecessarily during frame parsing operations, particularly when dealing with Huffman-encoded data that requires expensive decoding operations on the receiving end.
The technical exploitation of this vulnerability leverages the fundamental design of HTTP/2's header handling mechanism where all HEADERS and CONTINUATION frames must be parsed to maintain proper HPACK state, regardless of whether the resulting header data will ultimately be accepted or rejected. When an attacker sends a large number of CONTINUATION frames that collectively exceed the MaxHeaderBytes threshold, the system continues to process these frames without allocating additional memory for storage, but still performs the computational work of parsing and decoding the header data. This creates a computational overhead where the receiver must decode Huffman-encoded data that was never actually stored, leading to disproportionate resource consumption. The vulnerability is particularly dangerous because the decoding cost for Huffman-encoded data can be orders of magnitude higher than the network transmission cost, creating an asymmetric resource consumption attack vector.
The operational impact of CVE-2023-45288 extends beyond simple denial of service scenarios to potentially affect system availability and performance across multiple network services. Attackers can cause sustained resource exhaustion by maintaining connections with excessive header frames, leading to degraded performance or complete service unavailability for legitimate users. The vulnerability affects any HTTP/2 endpoint that properly implements HPACK state management, making it particularly concerning for web servers, reverse proxies, and load balancers that handle high volumes of HTTP/2 traffic. This attack can be executed with minimal resources from the attacker side while causing significant computational overhead on the target system, making it an attractive vector for resource exhaustion attacks in distributed environments.
Security mitigations for this vulnerability typically involve implementing connection-level limits on the number of header frames that can be processed beyond the maximum header size threshold. The recommended approach is to establish a reasonable limit on the amount of excess header data that will be processed before forcibly closing the connection, effectively preventing the accumulation of computational overhead. Organizations should also consider implementing rate limiting mechanisms for header frame processing and monitoring for unusual patterns of header frame accumulation. From a defensive perspective, this vulnerability aligns with CWE-400 weakness category related to resource exhaustion and demonstrates the importance of implementing proper bounds checking in protocol implementations. The fix essentially addresses the root cause by introducing a bounded computational complexity limit on header frame processing, preventing attackers from exploiting the quadratic resource consumption characteristics of HPACK state management. This vulnerability also relates to ATT&CK technique T1499.004 for resource exhaustion and highlights the critical need for proper input validation in network protocol implementations to prevent attackers from manipulating system resources through carefully crafted protocol messages.