Vulnerability · Published Feb 25, 2026 · Assigned by GitHub_M

CVE-2026-27730esm.sh has SSRF localhost/private-network bypass in `/http(s)` module route

High 8.6

In plain English

A high-severity server-side request forgery in esm.sh from esm-dev. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 33% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.0)8.6High

Exploit odds (30 days)0.4%top 67.1% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official description

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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Go	github.com/esm-dev/esm.sh	0.0.0-20250616164159-0593516c4cfa	GHSA-p2v6-84h2-5x4r
Go	github.com/esm-dev/esm.sh	0.0.0-20250616164159-0593516c4cfa	GO-2026-4554

Affected products (as reported)

Vendor	Product	Versions
esm-dev	esm.sh	<= 137

Weakness: CWE-918 · Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N

References

https://github.com/esm-dev/esm.sh/security/advisories/GHSA-p2v6-84h2-5x4r x_refsource_CONFIRM