felippe-regazio ssrfcheck up to 1.3.0 WHATWG URL Parser isSSRFSafeURL incomplete blacklist

Summaryinfo

A vulnerability, which was classified as critical, was found in felippe-regazio ssrfcheck up to 1.3.0. Impacted is the function isSSRFSafeURL of the component WHATWG URL Parser. Such manipulation leads to incomplete blacklist. This vulnerability is uniquely identified as CVE-2026-43929. The attack can be launched remotely. No exploit exists.

Detailsinfo

A vulnerability was found in felippe-regazio ssrfcheck up to 1.3.0. It has been rated as critical. Affected by this issue is the function isSSRFSafeURL of the component WHATWG URL Parser. The manipulation with an unknown input leads to a incomplete blacklist vulnerability. Using CWE to declare the problem leads to CWE-184. The product implements a protection mechanism that relies on a list of inputs (or properties of inputs) that are not allowed by policy or otherwise require other action to neutralize before additional processing takes place, but the list is incomplete, leading to resultant weaknesses. Impacted is confidentiality, integrity, and availability. CVE summarizes:

ssrfcheck is a library that checks if a string contains a potential SSRF attack. In 1.3.0 and earlier, ssrfcheck fails to block Server-Side Request Forgery attacks when the target private IP address is encoded as an IPv4-mapped IPv6 address (e.g. http://[::ffff:127.0.0.1]/). The WHATWG URL parser built into Node.js silently normalizes the IPv4 notation inside the brackets to compressed hex form ([::ffff:7f00:1]) before the library's private-IP regex ever runs. The regex was written to match dot-notation only and therefore never matches any real input — all seven IANA private IPv4 ranges, including the AWS/GCP/Azure metadata address 169.254.169.254, are bypassed. Any application using isSSRFSafeURL() to guard HTTP requests made with user-supplied URLs is fully exposed to SSRF.

The advisory is available at github.com. This vulnerability is handled as CVE-2026-43929 since 05/04/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. Technical details are known, but there is no available exploit. The structure of the vulnerability defines a possible price range of USD $0-$5k at the moment (estimation calculated on 05/12/2026). This vulnerability is assigned to T1562.006 by the MITRE ATT&CK project.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

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Productinfo

Vendor

• felippe-regazio

Name

• ssrfcheck

Version

• 1.0
• 1.1
• 1.2
• 1.3.0

Website

• Product: https://github.com/felippe-regazio/ssrfcheck/

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