VulnScan

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

What is CWE-918?

MITRE CWE

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.

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Official definition

MITRE CWE

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.

Detailed description

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Characteristics

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  • XSPA: Cross Site Port Attack
  • SSRF: Server-Side Request Forgery

Modes of introduction

  • Architecture and Design
  • Implementation

Common consequences

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  • Confidentiality

    Read Application Data

  • Integrity

    Execute Unauthorized Code or Commands

  • Access Control

    Bypass Protection Mechanism

    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.

Mitigations

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Detection methods

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  • Automated Static AnalysisAutomated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)Effectiveness: High

Representative vulnerabilities

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These examples illustrate this CWE entry and are not an exhaustive list of related vulnerabilities.

  • CVE-2026-33626SSRF in LLM toolkit accesses arbitrary URLs for images, as exploited in the wild in April 2026 to conduct port scanning [REF-1519]
  • CVE-2024-3095SSRF in LLM application development framework because the URL retriever allows connections to local addresses using a crafted Location header
  • CVE-2023-32786Chain: LLM integration framework has prompt injection (CWE-1427) that allows an attacker to force the service to retrieve data from an arbitrary URL, essentially providing SSRF (CWE-918) and potentially injecting content into downstream tasks.
  • CVE-2021-26855Server Side Request Forgery (SSRF) in mail server, as exploited in the wild per CISA KEV.
  • CVE-2021-21973Server Side Request Forgery in cloud platform, as exploited in the wild per CISA KEV.
  • CVE-2016-4029Chain: incorrect validation of intended decimal-based IP address format (CWE-1286) enables parsing of octal or hexadecimal formats (CWE-1389), allowing bypass of an SSRF protection mechanism (CWE-918).
  • CVE-2002-1484Web server allows attackers to request a URL from another server, including other ports, which allows proxied scanning.
  • CVE-2004-2061CGI script accepts and retrieves incoming URLs.
  • CVE-2010-1637Web-based mail program allows internal network scanning using a modified POP3 port number.
  • CVE-2009-0037URL-downloading library automatically follows redirects to file:// and scp:// URLs

Sources and references

References

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