Vulnerability · Published May 28, 2026 · Assigned by GitHub_M

CVE-2026-44593esm.sh: Legacy Route Path Traversal Can Lead to RCE

High 8.7

In plain English

A high-severity path traversal in esm.sh from esm-dev. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 38% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)8.7High

Exploit odds (30 days)0.4%top 61.9% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official description

esm.sh is a no-build content delivery network (CDN) for web development. In 137 and earlier, the legacy router first retrieves a response from legacyServer, parses the incoming request path, and ultimately writes the data to storage via buildStorage.Put. The router concatenates the path components without sanitizing them, producing a storage key. When this key is used, the underlying file system resolves the relative segments and writes the file to the specified path. Thus an attacker can craft a request that writes data to arbitrary locations on the server.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Go	github.com/esm-dev/esm.sh	0.0.0-20260508100112-1960055e1d53	GHSA-3636-h3vx-6465
Go	github.com/esm-dev/esm.sh	0.0.0-20260508100112-1960055e1d53	GO-2026-5071

Affected products (as reported)

Vendor	Product	Versions
esm-dev	esm.sh	<= 137

Weakness: CWE-22 · Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N

References

https://github.com/esm-dev/esm.sh/security/advisories/GHSA-3636-h3vx-6465 x_refsource_CONFIRM