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RFC 3875

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RFC 3875
RFC 3875
National Center for Supercomputing Applications · Public domain · source
Number3875
TitleCommon Gateway Interface (CGI) Version 1.1
AuthorIan F. Darwin, David G. Robinson
StatusProposed Standard
Year2004
OrganizationInternet Engineering Task Force

RFC 3875

RFC 3875 is the Internet Engineering Task Force specification that defines the Common Gateway Interface (CGI) Version 1.1, a protocol for interfacing external programs with information servers such as web servers. The document updates and consolidates prior practice around program-server interaction, environment variables, and input/output semantics to facilitate interoperability among implementations. It was produced within the IETF framework and influenced the way dynamic content is generated by linking server software to external applications.

Overview

RFC 3875 specifies the interaction between an external program and an information server to produce dynamic content, covering invocation, environment settings, request metadata, and response formatting. It formalizes behavior used in conjunction with software such as Apache HTTP Server, Netscape Communications Corporation, Microsoft IIS, and application frameworks created by authors associated with Perl, Python (programming language), and PHP. The specification describes standardized environment variables derived from Hypertext Transfer Protocol semantics and common operating system interfaces like POSIX to ensure predictable execution across platforms.

History and Development

The CGI concept originated in the early web era alongside projects like NCSA HTTPd and influenced implementations in servers associated with organizations such as National Center for Supercomputing Applications, Mosaic, and vendors including Sun Microsystems and IBM. RFC 3875 consolidated earlier de facto conventions and addressed divergent behaviors observed in implementations from groups like the World Wide Web Consortium community and contributors from the Internet Systems Consortium. Authors synthesized community experience from mailing lists, working groups, and software from contributors linked to OpenBSD, FreeBSD, and other open-source projects. The specification reflects interactions with standards such as RFC 2068 and RFC 2616 (versions of HTTP) and aligns with system interfaces influenced by IEEE and The Open Group.

Specification and Key Concepts

Key concepts in the document include the mapping of request metadata to environment variables, the delineation of standard input and output semantics, and the canonicalization of status and header management. The environment variables defined reference headers used in Hypertext Transfer Protocol exchanges and elements of URI syntax used in specifications like RFC 3986. The CGI program’s lifetime, process model, and I/O conventions assume operating environments exemplified by Unix-like systems and standards such as POSIX.1. Response formatting expectations correspond to conventions established in the Internet Assigned Numbers Authority registries and HTTP header handling practices implemented in Apache HTTP Server modules and extensions present in NGINX and other server projects.

Security Considerations

RFC 3875 highlights security implications related to environment variable trust, input validation, and process privilege handling, drawing attention to attack vectors familiar to administrators of servers like Microsoft IIS and Apache HTTP Server. It warns about header injection, path manipulation, and the risks of exposing credentials or internal filesystem layout, concerns also addressed in advisories from organizations such as CERT Coordination Center and teams at OpenSSL and GnuPG. The specification encourages least-privilege execution models similar to practices in SELinux and AppArmor deployments and suggests mitigation patterns consistent with recommendations from National Institute of Standards and Technology publications and incident response guidance from FIRST.

Implementations and Adoption

CGI as defined by RFC 3875 has been implemented across a wide array of web servers, scripting language runtimes, and application toolkits produced by communities and companies associated with Perl, Python (programming language), Ruby (programming language), PHP, Java (programming language), and .NET Framework. Popular server platforms including Apache HTTP Server, NGINX, Microsoft IIS, and embedded servers in products from Oracle Corporation and IBM support CGI or derivatives. While newer interfaces such as those promoted by FastCGI and application container models from organizations like Cloud Native Computing Foundation have supplemented CGI for performance reasons, RFC 3875 remains a reference point cited in documentation from projects maintained by contributors affiliated with Debian, Red Hat, and other distributions.

RFC 3875 interacts with standards in the HTTP family and URI specifications such as RFC 3986, as well as earlier HTTP specifications like RFC 2616. Extensions and alternatives that evolved alongside CGI include FastCGI, SCGI, and gateway mechanisms used in application servers implementing Java Servlet API and protocols employed by projects associated with WSGI for Python (programming language). Integration patterns informed by RFC 3875 influenced middleware and reverse-proxy designs implemented by organizations behind HAProxy, Varnish, and cloud providers whose architectures are discussed in materials by Amazon Web Services and Google Cloud Platform.

Category:Internet Standards