CVE-2026-27730

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

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

esm-dev · esm.sh

CVSS v3.1 NVD

7.5 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

CVSS v3.0 GITHUB

8.6 HIGHCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N

EPSS

0.48% chance of exploitation in the next 30 days, 40th percentile

Published

2026-02-25

Proof-of-concept exploits (1)

• advisories/GHSA-p2v6-84h2-5x4r

Security advisories

• esm-dev/esm.sh/security/advisories/GHSA-p2v6-84h2-5x4r

References

• CVE Record
• NVD entry