CVE-2017-1000118 in http
Summary
by MITRE
Akka HTTP versions <= 10.0.5 Illegal Media Range in Accept Header Causes StackOverflowError Leading to Denial of Service
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Analysis
by VulDB Data Team • 11/22/2019
The vulnerability CVE-2017-1000118 affects Akka HTTP server versions 10.0.5 and earlier, presenting a critical denial of service threat through malformed media range handling in HTTP Accept headers. This issue stems from improper validation of media type specifications within the Accept header field, which can trigger infinite recursion during request processing. The flaw specifically manifests when an attacker crafts an Accept header containing an illegal media range that causes the HTTP parser to enter a recursive loop while attempting to parse the malformed content. This recursive processing consumes excessive stack memory and ultimately results in a StackOverflowError, effectively crashing the application and rendering it unavailable to legitimate users. The vulnerability directly impacts the HTTP request handling pipeline where Akka HTTP processes incoming requests and validates their headers against expected formats.
The technical implementation of this vulnerability leverages the way Akka HTTP's media type parser handles wildcard and range specifications in Accept headers. When an attacker submits a request containing an Accept header with malformed media ranges such as nested wildcards or improperly structured content type specifications, the parser enters a recursive parsing loop. This recursive behavior occurs because the parser attempts to validate the media range against itself, creating an infinite loop that exhausts the available stack space. The stack overflow manifests as a java.lang.StackOverflowError exception, which is not properly handled by the application, leading to application termination and complete service unavailability. This parsing flaw represents a classic example of improper input validation and inadequate recursion depth checking, falling under CWE-674 for Uncontrolled Recursion and CWE-400 for Uncontrolled Resource Consumption.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be exploited by malicious actors to perform coordinated denial of service attacks against Akka HTTP applications. Attackers can craft minimal requests with carefully constructed Accept headers to trigger the stack overflow condition, requiring only basic HTTP client capabilities to execute. The vulnerability affects web applications built on Akka HTTP that process user-provided Accept headers, making it particularly dangerous for public-facing services, APIs, and web applications that rely on this framework. The attack vector is particularly insidious because it requires no authentication or special privileges, making it accessible to any attacker who can send HTTP requests to the target system. This vulnerability can be exploited to bring down entire application instances, potentially affecting multiple users or services depending on the application architecture.
Mitigation strategies for CVE-2017-1000118 focus primarily on upgrading to patched versions of Akka HTTP, specifically versions 10.0.6 and later where the media type parsing logic has been corrected to prevent recursive parsing behavior. Organizations should immediately implement this upgrade across all affected systems and verify that the patch resolves the stack overflow condition. Additional defensive measures include implementing request rate limiting and input validation at reverse proxies or load balancers to detect and block malformed Accept headers before they reach the application servers. Network-level filtering can also be employed to restrict the size and complexity of Accept headers processed by the application. Security teams should monitor application logs for patterns indicating potential exploitation attempts and implement proper error handling to prevent unhandled stack overflow exceptions from causing application crashes. The vulnerability demonstrates the importance of proper input validation and recursion control mechanisms in web application frameworks, aligning with ATT&CK technique T1499.004 for Network Denial of Service and emphasizing the need for robust parsing implementations that cannot be easily exploited through malformed input.