CVE-2017-7656 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), HTTP/0.9 is handled poorly. An HTTP/1 style request line (i.e. method space URI space version) that declares a version of HTTP/0.9 was accepted and treated as a 0.9 request. If deployed behind an intermediary that also accepted and passed through the 0.9 version (but did not act on it), then the response sent could be interpreted by the intermediary as HTTP/1 headers. This could be used to poison the cache if the server allowed the origin client to generate arbitrary content in the response.
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Analysis
by VulDB Data Team • 03/28/2023
The vulnerability identified as CVE-2017-7656 affects Eclipse Jetty web server implementations across multiple version branches including 9.2.x and older, 9.3.x in all configurations, and 9.4.x when operating with non-default RFC2616 compliance settings. This issue stems from improper handling of HTTP/0.9 protocol requests within the server's request parsing logic, creating a significant security risk that can be exploited through intermediary proxy servers. The flaw manifests when an HTTP/1 style request line containing a version declaration of HTTP/0.9 is processed by the server, causing the system to treat it as an HTTP/0.9 request despite the method and URI format following HTTP/1.0 conventions. This misclassification occurs because the server fails to properly validate the version string against the expected HTTP/0.9 protocol specification, which typically uses a simpler request format without version information.
The operational impact of this vulnerability becomes particularly dangerous when the affected Jetty server operates behind intermediary devices such as reverse proxies or content delivery networks that also accept HTTP/0.9 version declarations but do not properly process them. When a malicious request is sent with an HTTP/0.9 version string but HTTP/1.0 format, the server processes it as an HTTP/0.9 request and generates a response. However, if this response passes through an intermediary that treats the response as HTTP/1.0 headers, the intermediary may interpret the response content incorrectly, leading to cache poisoning attacks. This behavior creates a fundamental mismatch between how the origin server and the intermediary handle the same response, allowing an attacker to inject malicious content into the cache that will be served to other users. The vulnerability is particularly concerning because it can be exploited even with standard HTTP/1.0 request formats, making it difficult to detect through conventional security scanning methods.
The technical flaw represents a protocol parsing inconsistency that violates the principle of proper input validation and request handling as outlined in CWE-20, which addresses "Improper Input Validation." This vulnerability also aligns with ATT&CK technique T1071.004, "Application Layer Protocol: DNS," and T1566, "Phishing," as it enables attackers to manipulate responses that are cached and subsequently delivered to users. The improper handling of HTTP version strings creates a path for response manipulation that can be leveraged for cache poisoning attacks, where malicious content injected into cached responses can be served to multiple users simultaneously. Security researchers have noted that this vulnerability is particularly dangerous in environments where caching intermediaries are present, as the attack can propagate beyond the immediate server to affect all users served through those intermediaries. The risk is exacerbated by the fact that the vulnerability exists in widely deployed versions of Jetty, making it a significant concern for organizations with extensive web server infrastructure.
Organizations should implement immediate mitigations including upgrading to patched versions of Eclipse Jetty where available, configuring the server to disable RFC2616 compliance for HTTP/0.9 handling when not required, and implementing proper request validation mechanisms that enforce strict protocol compliance. Network administrators should also consider deploying additional security controls such as web application firewalls that can detect and block malformed HTTP requests, and implementing proper cache invalidation procedures to prevent poisoned cache entries from serving malicious content. The vulnerability demonstrates the importance of maintaining strict protocol compliance in web server implementations and highlights the risks associated with improper handling of legacy protocol versions in modern web environments where multiple layers of intermediaries may be present. Organizations should also conduct thorough security assessments of their web server configurations to ensure that no other similar protocol handling issues exist within their infrastructure, particularly in systems that may be vulnerable to similar cache poisoning or response manipulation attacks.