esm.sh: web.NewHandler allows arbitrary file read via encoded dot-segment path traversal
Affects esm.sh using the web.NewHandler static file server with Config.AppDir set, when request paths contain URL-encoded dot-segments. Fixed in 137_7.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
- Exploited
- No known exploitation
- Fix
- Fixed in 137_7
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 137_7.
- Last modified
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 25/100 · provisional
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Unclear
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
esm.sh, a no-build content delivery network for web development, has a path traversal flaw in its static file server (web.NewHandler). Remotely, without logging in, an attacker can use URL-encoded dot segments in a request path to read files outside the application directory that the server process can access.
Read the original description
esm.sh is a no-build content delivery network (CDN) for web development. Prior to server version 137_7, the documented web.NewHandler static file server in web/handler.go joins the URL-decoded r.URL.Path with Config.AppDir without verifying that the result remains inside the configured application directory. URL-encoded dot segments such as %2e%2e bypass the plain traversal redirect performed by Go's ServeMux, allowing an unauthenticated remote attacker to make the server open and return files outside Config.AppDir that are readable by the server process. The confirmed impact is file disclosure only, and the issue is reachable with Dev disabled. This issue is fixed in server version 137_7.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure17/25No login or user action needed, reachable over the network without a login · Unknown: Advisories don't say whether default setups are affected
- Reach?/20Unknown. No tracked technology or package matched
- Severity7.5/10CVSS 7.5
- No patch0/5No signal
What would change the score
- Would score about 70 if added to CISA KEV
- Would score about 65 if CISA's SSVC rates exploitation active
- Would score about 30 if advisories confirm default setups are exposed
What to do
Upgrade to a fixed version: 137_7.
Timeline
- CVE published
- First seen by cve.now
Affected versions
- esm-dev esm.sh
fixed in 137_7
Evidence 5
- Advisory
- Repository
- Repository
- Repository
- Repository
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-102657
Is CVE-2026-102657 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
What does this mean?
A request path with URL-encoded dot-segments such as %2e%2e can make the static file server read files outside the configured web application directory. Those can include source, configuration, or credential files that the server process can read, and no login is needed to send the request.Source: github.com
Which versions are affected by CVE-2026-102657?
esm.sh: before 137_7.Source: cve.now feed data
Am I affected, and how do I check?
The bug involves the documented web.NewHandler static file server with Config.AppDir set, and it reproduces with Dev disabled. To check a setup, look at whether the application uses web.NewHandler with Config.AppDir set, and compare the esm.sh version against 137_7.Source: github.com
How do I fix CVE-2026-102657?
Upgrade esm.sh to 137_7 or later, the fixed version listed for this issue.Source: github.com