Common Weakness Enumeration

A Community-Developed List of Software Weakness Types

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CWE-918: Server-Side Request Forgery (SSRF)

Weakness ID: 918
Abstraction: Base
Structure: Simple
Status: Incomplete
Presentation Filter:
+ Description
The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.
+ Extended Description
By providing URLs to unexpected hosts or ports, attackers can make it appear that the server is sending the request, possibly bypassing access controls such as firewalls that prevent the attackers from accessing the URLs directly. The server can be used as a proxy to conduct port scanning of hosts in internal networks, use other URLs such as that can access documents on the system (using file://), or use other protocols such as gopher:// or tftp://, which may provide greater control over the contents of requests.
+ Alternate Terms
Cross Site Port Attack
+ Relationships

The table(s) below shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.

+ Relevant to the view "Research Concepts" (CWE-1000)
+ Relevant to the view "Weaknesses for Simplified Mapping of Published Vulnerabilities" (CWE-1003)
+ Relevant to the view "Development Concepts" (CWE-699)
MemberOfCategoryCategory442Web Problems
ChildOfClassClass441Unintended Proxy or Intermediary ('Confused Deputy')
+ Modes Of Introduction

The different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the software life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.

Architecture and Design
+ Applicable Platforms
The listings below show possible areas for which the given weakness could appear. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. The platform is listed along with how frequently the given weakness appears for that instance.


Class: Language-Independent (Undetermined Prevalence)


Web Based (Undetermined Prevalence)


Web Server (Undetermined Prevalence)

+ Common Consequences

The table below specifies different individual consequences associated with the weakness. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a weakness will be exploited to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.


Technical Impact: Read Application Data


Technical Impact: Execute Unauthorized Code or Commands

+ Observed Examples
Web server allows attackers to request a URL from another server, including other ports, which allows proxied scanning.
CGI script accepts and retrieves incoming URLs.
Web-based mail program allows internal network scanning using a modified POP3 port number.
URL-downloading library automatically follows redirects to file:// and scp:// URLs
+ Notes


CWE-918 (SSRF) and CWE-611 (XXE) are closely related, because they both involve web-related technologies and can launch outbound requests to unexpected destinations. However, XXE can be performed client-side, or in other contexts in which the software is not acting directly as a server, so the "Server" portion of the SSRF acronym does not necessarily apply.
+ References
[REF-913] Alexander Polyakov and Dmitry Chastukhin. "SSRF vs. Business-critical applications: XXE tunneling in SAP". 2012-07-26. <>.
[REF-914] Alexander Polyakov, Dmitry Chastukhin and Alexey Tyurin. "SSRF vs. Business-critical Applications. Part 1: XXE Tunnelling in SAP NetWeaver". <>.
[REF-915] Riyaz Ahemed Walikar. "Cross Site Port Attacks - XSPA - Part 1". 2012-11-07. <>.
[REF-916] Riyaz Ahemed Walikar. "Cross Site Port Attacks - XSPA - Part 2". 2012-11-13. <>.
[REF-917] Riyaz Ahemed Walikar. "Cross Site Port Attacks - XSPA - Part 3". 2012-11-14. <>.
[REF-918] Vladimir Vorontsov and Alexander Golovko. "SSRF attacks and sockets: smorgasbord of vulnerabilities". <>.
[REF-919] ONsec Lab. "SSRF bible. Cheatsheet". 2013-01-26. <>.
[REF-920] Deral Heiland. "Web Portals: Gateway To Information, Or A Hole In Our Perimeter Defenses". 2008-02. <,%20gateway%20to%20information.ppt>.
+ Content History
Submission DateSubmitterOrganization
2013-02-17CWE Content TeamMITRE
Modification DateModifierOrganization
2015-12-07CWE Content TeamMITRE
updated Relationships
2017-01-19CWE Content TeamMITRE
updated Relationships
2017-11-08CWE Content TeamMITRE
updated Applicable_Platforms, References

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Page Last Updated: January 18, 2018