What is CVE-2026-27730?

CVE-2026-27730 is a high-severity vulnerability in Esm Esm.sh, classified under Server-Side Request Forgery (SSRF). CVSS score: 7.5/10. Published 2026-02-25.

How severe is CVE-2026-27730?

High severity. CVSS v3 base score is 7.5 out of 10.

SSRF in Esm Esm.sh

CVE-2026-27730

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.

Vulnerability class: SSRF (Server-Side Request Forgery)

EPSS: 0.003 (26.5th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N.

Affected products

Esm Esm.sh
Esm-dev Esm.sh — versions <= 137

Weakness classification (CWE)

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

References

security-advisories@github.com (x_refsource_CONFIRM, Exploit, Vendor Advisory)

Frequently asked questions

What is CVE-2026-27730?: CVE-2026-27730 is a high-severity vulnerability in Esm Esm.sh, classified under Server-Side Request Forgery (SSRF). CVSS score: 7.5/10. Published 2026-02-25.
How severe is CVE-2026-27730?: High severity. CVSS v3 base score is 7.5 out of 10.