CWE

Common Weakness Enumeration

A Community-Developed List of Software & Hardware Weakness Types

CWE Top 25 Most Dangerous Weaknesses
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ID

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
XSPA:
Cross Site Port Attack
+ Relationships
Section HelpThis table 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)
NatureTypeIDName
ChildOfClassClass - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.441Unintended Proxy or Intermediary ('Confused Deputy')
Section HelpThis table 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 "Weaknesses for Simplified Mapping of Published Vulnerabilities" (CWE-1003)
NatureTypeIDName
ChildOfClassClass - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.610Externally Controlled Reference to a Resource in Another Sphere
+ Modes Of Introduction
Section HelpThe different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.
PhaseNote
Architecture and Design
Implementation
+ Applicable Platforms
Section HelpThis listing shows 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.

Languages

Class: Language-Independent (Undetermined Prevalence)

Technologies

Web Server (Undetermined Prevalence)

+ Common Consequences
Section HelpThis table 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.
ScopeImpactLikelihood
Confidentiality

Technical Impact: Read Application Data

Integrity

Technical Impact: Execute Unauthorized Code or Commands

+ Observed Examples
ReferenceDescription
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
+ Memberships
Section HelpThis MemberOf Relationships table shows additional CWE Categories and Views that reference this weakness as a member. This information is often useful in understanding where a weakness fits within the context of external information sources.
NatureTypeIDName
MemberOfViewView - a subset of CWE entries that provides a way of examining CWE content. The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries).1337Weaknesses in the 2021 CWE Top 25 Most Dangerous Software Weaknesses
+ Notes

Relationship

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. <https://media.blackhat.com/bh-us-12/Briefings/Polyakov/BH_US_12_Polyakov_SSRF_Business_Slides.pdf>.
[REF-914] Alexander Polyakov, Dmitry Chastukhin and Alexey Tyurin. "SSRF vs. Business-critical Applications. Part 1: XXE Tunnelling in SAP NetWeaver". <http://erpscan.com/wp-content/uploads/2012/08/SSRF-vs-Businness-critical-applications-whitepaper.pdf>.
[REF-915] Riyaz Ahemed Walikar. "Cross Site Port Attacks - XSPA - Part 1". 2012-11-07. <https://ibreak.software/2012/11/cross-site-port-attacks-xspa-part-1/>.
[REF-916] Riyaz Ahemed Walikar. "Cross Site Port Attacks - XSPA - Part 2". 2012-11-13. <https://ibreak.software/2012/11/cross-site-port-attacks-xspa-part-2/>.
[REF-917] Riyaz Ahemed Walikar. "Cross Site Port Attacks - XSPA - Part 3". 2012-11-14. <https://ibreak.software/2012/11/cross-site-port-attacks-xspa-part-3/>.
[REF-918] Vladimir Vorontsov and Alexander Golovko. "SSRF attacks and sockets: smorgasbord of vulnerabilities". <http://www.slideshare.net/d0znpp/ssrf-attacks-and-sockets-smorgasbord-of-vulnerabilities>.
[REF-919] ONsec Lab. "SSRF bible. Cheatsheet". 2013-01-26. <https://docs.google.com/document/d/1v1TkWZtrhzRLy0bYXBcdLUedXGb9njTNIJXa3u9akHM/edit?pli=1#>.
[REF-920] Deral Heiland. "Web Portals: Gateway To Information, Or A Hole In Our Perimeter Defenses". 2008-02. <http://www.shmoocon.org/2008/presentations/Web%20portals,%20gateway%20to%20information.ppt>.
+ Content History
+ Submissions
Submission DateSubmitterOrganization
2013-02-17CWE Content TeamMITRE
+ Modifications
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
2018-03-27CWE Content TeamMITRE
updated References
2019-06-20CWE Content TeamMITRE
updated Relationships
2020-02-24CWE Content TeamMITRE
updated Applicable_Platforms, Relationships
2021-07-20CWE Content TeamMITRE
updated References, Related_Attack_Patterns, Relationships
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Page Last Updated: July 20, 2021