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

> Attackers can exploit path traversal in the legacy router to write arbitrary files, potentially leading to remote code execution on the esm.sh server.

- **Severity:** High 8.7 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 28 May 2026
- **Updated:** 2 Jun 2026
- **Also known as:** GHSA-3636-h3vx-6465, GO-2026-5071

## What is CVE-2026-44593?

CVE-2026-44593 is a high-severity path traversal vulnerability in esm-dev esm.sh, published on 28 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### 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.

Weakness: CWE-22 (Improper Limitation of a Pathname to a Restricted Directory)

## Which versions are affected by CVE-2026-44593?

3 open source packages ship an affected version, including github.com/esm-dev/esm.sh.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/esm-dev/esm.sh` | Go | All versions | 0.0.0-20260508100112-1960055e1d53 |
| `github.com/esm-dev/esm.sh` | Go | All versions | 0.0.0-20260508100112-1960055e1d53 |
| `github.com/esm-dev/esm.sh` | Go | All versions | 0.0.0-20260508100112-1960055e1d53 |

## How do I fix CVE-2026-44593?

Upgrade github.com/esm-dev/esm.sh to 0.0.0-20260508100112-1960055e1d53 or later.

## Is CVE-2026-44593 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-44593 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-44593 and fix it if it is affected.

What it is: CVE-2026-44593 is a high-severity path traversal vulnerability in esm-dev esm.sh, published on 28 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-44593 exists.

Affected packages and fixed versions:
- github.com/esm-dev/esm.sh (Go): affected all versions; fixed in 0.0.0-20260508100112-1960055e1d53
- github.com/esm-dev/esm.sh (Go): affected all versions; fixed in 0.0.0-20260508100112-1960055e1d53
- github.com/esm-dev/esm.sh (Go): affected all versions; fixed in 0.0.0-20260508100112-1960055e1d53

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-44593/ (Markdown: https://insights.sbomify.com/CVE-2026-44593/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-44593
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-44593
- OSV: https://osv.dev/vulnerability/CVE-2026-44593

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-44593/
Summaries are generated and may contain mistakes; the official description above is the record.