CVE-2026-27730CWE-918

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

High · published February 25, 2026

CVSS v3.0
8.6
EPSS
0%
Percentile
40.8
In the wild
Unconfirmed
What it 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.

The record
Technical detail
CVSS v3.0
8.6 · HIGH
Vector
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N
CVSS v4.0
Not supplied
EPSS
0.00485 · 40.8th percentile
Weakness
CWE-918 · Server-Side Request Forgery (SSRF)
Published
2026-02-25T15:37Z
EPSS history
Timeline
  • 25 FEB 15:37Z
    esm.sh has SSRF localhost/private-network bypass in `/http(s)` module route
    cvelistv5