esm-dev esm.sh up to 137 server-side request forgery

Summaryinfo

A vulnerability was found in esm-dev esm.sh up to 137. It has been rated as critical. This affects an unknown function. The manipulation leads to server-side request forgery. This vulnerability is referenced as CVE-2026-27730. Remote exploitation of the attack is possible. No exploit is available.

Detailsinfo

A vulnerability was found in esm-dev esm.sh up to 137. It has been rated as critical. This issue affects an unknown function. The manipulation with an unknown input leads to a server-side request forgery vulnerability. Using CWE to declare the problem leads to CWE-918. 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. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

esm.sh is a no-build content delivery network (CDN) for web development. Versions up to and including 137 have an SSRF vulnerability (CWE-918) in esm.sh’s `/http(s)` fetch route. The service tries to block localhost/internal targets, but the validation is based on hostname string checks and can be bypassed using DNS alias domains. This allows an external requester to make the esm.sh server fetch internal localhost services. As of time of publication, no known patched versions exist.

It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-27730 since 02/23/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. The technical details are unknown and an exploit is not publicly available. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 02/28/2026).

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

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-8685). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Productinfo

Vendor

• esm-dev

Name

• esm.sh

Version

• 137

Website

• Product: https://github.com/esm-dev/esm.sh/

CPE 2.3info

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CPE 2.2info

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Entryinfo

Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

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