High severity · published Feb 25, 2026
CVE-2026-27730
esm.sh has SSRF localhost/private-network bypass in `/http(s)` module route
7.5
CVSS
0.4%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
High
Integrity
None
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.4% · higher than 33% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
ES
esm.sh · esm-dev
<= 137 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-27730
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-27730
Exploit
https://github.com/esm-dev/esm.sh/security/advisories/GHSA-p2v6-84h2-5x4r
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