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ssrfcheck: SSRF Bypass Caused by Failure to Classify Reserved IP Address Space as Invalid

High severity GitHub Reviewed Published Apr 26, 2026 in felippe-regazio/ssrfcheck

Package

npm ssrfcheck (npm)

Affected versions

< 1.2.0

Patched versions

1.2.0

Description

SSRF Bypass in ssrfcheck - fails to classify reserved IP address space as invalid

ssrfcheck is an npm package that serves to provide protection from SSRF by validating URLs or hostname inputs.

Resources:

Vulnerability

The ssrfcheck package maintains a denylist of IP addresses and ranges to check against when validating if an IP address is to be considered as safe or not.

However, the IP address list used for the denylist is incomplete and misses a reserved IP address space as defined by the IANA (Internet Assigned Numbers Authority):

  • 224.0.0.0/4 - Multicast

Practically, this reserved IP address space is used for multicast traffic and would most commonly be used for reserved local communication over network protocols such as UDP, which would make it less likely to be used in a typical SSRF attack in practice.

However, such reserved IP address space shouldn't be allowed and it would be responsible of the SSRF protection package to align and conform to an agreed-upon standard of special-purposed addresses that should not be considered a valid public IP address. For reference, the popular npm packages private-ip and ipaddr.js that are highly dependent-upon to make decisions about SSRF protection and both consider the above mentioned IP address space as reserved and is not considered a valid public IP address.

Exploit Proof of Concept

  1. Install the ssrfcheck package:
npm install ssrfcheck
  1. Define an app.js file with the programmatic API of ssrfcheck:
import { isSSRFSafeURL } from 'ssrfcheck';

let result
result = isSSRFSafeURL('https://012.1.2.3/whatever');
console.log(result);  // returns false
result = isSSRFSafeURL('https://localhost:8080/whatever');
console.log(result);  // returns false

result = isSSRFSafeURL('https://239.255.255.250:8080/whatever');
console.log(result);  // returns true - bypassed

Vulnerable versions

All versions of ssrfcheck are vulnerable to this issue, up to and including to the latest version of 1.1.1.

Assigned CVE

CVE-2025-8267

Author

Liran Tal

References

@felippe-regazio felippe-regazio published to felippe-regazio/ssrfcheck Apr 26, 2026
Published to the GitHub Advisory Database May 5, 2026
Reviewed May 5, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity Low
Attack Requirements None
Privileges Required None
User interaction None
Vulnerable System Impact Metrics
Confidentiality High
Integrity Low
Availability None
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N/E:P

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(37th percentile)

Weaknesses

Server-Side Request Forgery (SSRF)

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. Learn more on MITRE.

CVE ID

CVE-2025-8267

GHSA ID

GHSA-p4hc-9pjh-55c8

Source code

Credits

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