CVE-2017-5850 in OpenBSD
Summary
by MITRE
httpd in OpenBSD allows remote attackers to cause a denial of service (memory consumption) via a series of requests for a large file using an HTTP Range header.
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Analysis
by VulDB Data Team • 08/01/2025
The vulnerability identified as CVE-2017-5850 affects the httpd implementation in OpenBSD operating systems, representing a significant denial of service weakness that can be exploited remotely. This flaw specifically targets the handling of HTTP Range headers when requesting large files, creating a scenario where malicious actors can consume excessive system memory resources through carefully crafted sequences of requests. The vulnerability resides in the web server's processing logic for partial content requests, which fails to properly manage memory allocation during range header processing. Attackers can leverage this weakness by sending multiple HTTP requests with Range headers that specify overlapping or excessively large byte ranges within a single file, causing the httpd process to allocate progressively more memory without proper bounds checking or resource limiting mechanisms.
The technical implementation of this vulnerability stems from inadequate input validation and memory management within the httpd server's range request handling code. When processing HTTP Range headers, the system does not properly validate the boundaries specified in these headers or enforce reasonable limits on memory allocation for partial content responses. This allows an attacker to craft requests that cause the server to continuously allocate memory for response buffers without sufficient garbage collection or memory reclamation processes. The flaw operates at the application layer within the HTTP protocol implementation, specifically targeting the server's response generation mechanism for range requests. According to CWE classification, this vulnerability maps to CWE-400, which covers "Uncontrolled Resource Consumption" or "Resource Exhaustion" conditions, while the ATT&CK framework would categorize this under T1499.004 for "Endpoint Denial of Service" techniques that exploit resource exhaustion vulnerabilities.
The operational impact of CVE-2017-5850 extends beyond simple service disruption, as it can lead to complete system instability and potential denial of service for legitimate users. When exploited successfully, the vulnerability causes the httpd process to consume increasing amounts of memory until system resources are exhausted, potentially leading to system crashes or requiring manual intervention to restart the web service. This type of attack can be particularly damaging in production environments where web servers handle critical business operations, as it can effectively shut down website availability and compromise service level agreements. The vulnerability affects systems running OpenBSD versions that include the affected httpd implementation, making it relevant to organizations maintaining older OpenBSD releases or those that have not applied the necessary security patches. Network administrators should consider this vulnerability as part of their broader denial of service threat modeling, particularly in environments where external access to web servers is permitted without proper rate limiting or resource monitoring mechanisms.
Mitigation strategies for CVE-2017-5850 should include immediate patching of affected OpenBSD systems with the latest security updates from the OpenBSD project, which typically address the memory allocation issues in range header processing. Organizations should implement rate limiting and connection throttling mechanisms to prevent abuse of the httpd service, particularly for range requests that might trigger excessive memory consumption. Network-level firewalls and intrusion detection systems can be configured to monitor for suspicious patterns of range header usage and automatically block or limit requests that exceed reasonable thresholds. Additionally, system administrators should enable memory monitoring and alerting mechanisms to detect when httpd processes begin consuming excessive resources, allowing for proactive intervention before complete service disruption occurs. The implementation of proper input validation and resource management practices within the web server configuration, including setting limits on the maximum size of range requests and the number of concurrent range operations, provides additional defense-in-depth measures. Organizations should also consider implementing application-level firewalls or reverse proxies that can filter and normalize HTTP requests before they reach the vulnerable httpd implementation, providing an additional layer of protection against this specific type of resource exhaustion attack.