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)
Published · last modified .
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.
EPSS exploit prediction
EPSS: 0.005 (38.6th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 39th percentile — 38.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.005 · change: +0.001
Affected products
- Esm Esm.sh
- Esm-Dev Esm.sh — versions <= 137
Weakness classification (CWE)
References
- github.com/esm-dev/esm.sh/security/advisories/GHSA-p2v6-84h2-5x4r (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.