CVE-2026-27730: high-severity vulnerability in esm-dev esm.sh
esm.sh has SSRF localhost/private-network bypass in `/http(s)` module route
Published
E-mail alert when it lands in KEV, gets a public PoC or its score goes up.
21Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 8.6epss 0.4%
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:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N
Affected products
esm-dev · esm.shRelated CVEs — esm-dev esm.sh
In the same product, most dangerous first.
CVE-2025-59342MEDIUMesm.sh writes arbitrary files via path traversal in `X-Zone-Id` headerEPSS 3.2%CVE-2025-59341HIGHLocal File Inclusion in esm.shEPSS 1.6%CVE-2026-102657HIGHesm.sh: web.NewHandler allows arbitrary file read via encoded dot-segment path traversalEPSS 0.7%CVE-2025-65025HIGHesm.sh CDN service has arbitrary file write via tarslipEPSS 0.6%CVE-2026-23644HIGHesm.sh has path traversal in `extractPackageTarball` that enables file writes from malicious packagesEPSS 0.6%CVE-2025-65026MEDIUMesm.sh CDN service has JS Template Literal Injection in CSS-to-JavaScriptEPSS 0.5%