CVE-2017-7657 in Jetty
Summary
by MITRE
In Eclipse Jetty, versions 9.2.x and older, 9.3.x (all configurations), and 9.4.x (non-default configuration with RFC2616 compliance enabled), transfer-encoding chunks are handled poorly. The chunk length parsing was vulnerable to an integer overflow. Thus a large chunk size could be interpreted as a smaller chunk size and content sent as chunk body could be interpreted as a pipelined request. If Jetty was deployed behind an intermediary that imposed some authorization and that intermediary allowed arbitrarily large chunks to be passed on unchanged, then this flaw could be used to bypass the authorization imposed by the intermediary as the fake pipelined request would not be interpreted by the intermediary as a request.
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Analysis
by VulDB Data Team • 03/28/2023
The vulnerability identified as CVE-2017-7657 affects Eclipse Jetty web servers across multiple version lines including 9.2.x, 9.3.x, and 9.4.x when specific configurations are employed. This issue stems from improper handling of HTTP transfer-encoding chunks within the server's HTTP parser implementation. The core technical flaw manifests as an integer overflow during chunk length parsing operations, creating a critical security weakness that can be exploited to manipulate HTTP request processing. The vulnerability specifically targets the HTTP chunked transfer encoding mechanism which is used to transfer data in a series of chunks rather than as a single contiguous block, a common practice in HTTP/1.1 implementations for handling large data transfers.
The operational impact of this vulnerability extends beyond simple parsing errors as it enables a sophisticated attack pattern where malicious actors can craft specially formatted HTTP requests that exploit the integer overflow to manipulate how chunk sizes are interpreted. When a large chunk size value is processed, the integer overflow causes the server to interpret this large value as a much smaller chunk size, effectively allowing attackers to manipulate the boundary conditions between HTTP chunks. This manipulation creates a scenario where content that should be treated as chunk body data gets misinterpreted as part of a subsequent pipelined HTTP request. The vulnerability becomes particularly dangerous when Jetty operates behind intermediary proxies or authentication systems that do not properly validate chunk sizes, as these intermediaries may pass through maliciously crafted chunks without inspection.
This vulnerability aligns with CWE-190, Integer Overflow or Wraparound, which classifies the underlying cause of the issue as improper handling of integer arithmetic operations that can result in unexpected behavior when values exceed their maximum representable range. From an attack perspective, the vulnerability maps to techniques described in the MITRE ATT&CK framework under T1071.004 Application Layer Protocol and T1566 Phishing, as it enables attackers to bypass authentication mechanisms by crafting HTTP requests that appear legitimate to the intermediary proxy but are misinterpreted by the backend Jetty server. The security implications are particularly severe in environments where Jetty serves as a backend for applications that rely on intermediary authorization systems, as attackers can potentially escalate privileges or gain unauthorized access to protected resources by exploiting this chunk parsing vulnerability.
The specific conditions required for exploitation involve a combination of factors including deployment of vulnerable Jetty versions behind intermediaries that allow large chunks to pass through unchanged, and the presence of authorization mechanisms that depend on proper HTTP parsing. Organizations should note that the vulnerability affects not only the default configurations but also non-default setups where RFC2616 compliance is explicitly enabled, making it a broad concern for Jetty deployments. Mitigation strategies include upgrading to patched versions of Jetty where the integer overflow has been addressed, implementing proper input validation for chunk sizes at intermediary proxies, and configuring security controls that limit the maximum chunk size allowed through the system. The vulnerability demonstrates the importance of proper integer handling in network protocol implementations and highlights the risks associated with complex HTTP parsing logic that must account for various edge cases in data processing.