## Affected Versions

version ≤ 2.7.8 (latest version at time of disclosure)

https://github.com/openmrs/openmrs-core

## Impact

The endpoint `POST /openmrs/ws/rest/v1/module` is vulnerable to a path traversal (Zip Slip) attack. An authenticated attacker can upload a crafted `.omod` archive containing ZIP entries with directory traversal sequences. Upon automatic extraction by the server, the incomplete path validation in `WebModuleUtil.startModule()` fails to prevent entries such as `web/module/../../../../malicious.jsp` from being written outside the intended module directory. If the traversal target falls within the web application root (e.g., `/usr/local/tomcat/webapps/openmrs/`), the attacker achieves arbitrary file write and subsequent Remote Code Execution.

Notably, other extraction methods in the same codebase (`ModuleUtil.expandJar()`, `TestInstallUtil.addZippedTestModules()`) are properly protected with `normalize().startsWith()` checks — this vulnerability is an oversight where the same fix was not applied.

Furthermore, the `module.allow_web_admin` runtime property, which is intended to restrict administrators from managing modules via the web interface, only gates the Legacy UI controller entry point. The REST API endpoint `POST /openmrs/ws/rest/v1/module` does not check this property, allowing this restriction to be fully bypassed.

## Steps to Reproduce

1. Construct a malicious `.omod` file (which is a ZIP/JAR archive) containing a ZIP entry with a path traversal payload in its entry name, such as `web/module/../../../../<target_filename>`. Upload this file to `POST /openmrs/ws/rest/v1/module` with valid admin credentials via Basic Auth.

<img width="1986" height="1102" alt="image" src="https://github.com/user-attachments/assets/647f15de-7e8c-40b9-aba9-d4db5d2e0b52" />

<img width="2048" height="1078" alt="image" src="https://github.com/user-attachments/assets/301412a0-e3b0-4afb-91c2-e9739de3080d" />


2. The server parses and loads the module. During `WebModuleUtil.startModule()`, entries under `web/module/` are automatically extracted. The existing check `Paths.get(name).startsWith("..")` only blocks entries beginning with `..`, so an entry starting with `web/module/` passes the check. The `../` sequences in the remaining path cause the file to be written outside the intended `WEB-INF/view/module/` directory — for example, into the web application root at `/usr/local/tomcat/webapps/openmrs/`.

<img width="1439" height="141" alt="image" src="https://github.com/user-attachments/assets/4bda3b1e-a80e-42ed-af2b-a1da53e8db03" />

3. The traversed file is now accessible under the web application root. If the written file is a JSP script, accessing it via the browser triggers server-side execution, achieving RCE.

<img width="1482" height="300" alt="image" src="https://github.com/user-attachments/assets/61936002-78cd-4203-80f0-f0a8702b216c" />

## Root Cause Analysis

The vulnerability exists in `WebModuleUtil.startModule()` (`web/src/main/java/org/openmrs/module/web/WebModuleUtil.java`).

### Vulnerable code:

```java
Enumeration<JarEntry> entries = jarFile.entries();
while (entries.hasMoreElements()) {
JarEntry entry = entries.nextElement();
String name = entry.getName();

// ❌ Incomplete check — only blocks entries starting with ".."
if (Paths.get(name).startsWith("..")) {
throw new UnsupportedOperationException("...");
}

if (name.startsWith("web/module/")) {
String filepath = name.substring(11);
StringBuilder absPath = new StringBuilder(realPath + "/WEB-INF");
absPath.append("/view/module/");
absPath.append(mod.getModuleIdAsPath()).append("/").append(filepath);

// ❌ No normalize() or startsWith() boundary check before writing
File outFile = new File(absPath.toString().replace("/", File.separator));
outStream = new FileOutputStream(outFile, false);
inStream = jarFile.getInputStream(entry);
OpenmrsUtil.copyFile(inStream, outStream);
}
}
```

**Why the check fails:** For an entry named `web/module/foo/../../../../evil.jsp`, `Paths.get(name)` starts with `web`, not `..`, so the check passes. After `name.substring(11)`, the filepath `foo/../../../../evil.jsp` is concatenated directly into the output path without normalization, resulting in a write outside the intended directory.

### Correctly protected code in the same codebase:

**`ModuleUtil.expandJar()`:**

```java
// ✅ Correct — uses normalize().startsWith()
if (!parent.toPath().normalize().startsWith(docBase)) {
throw new UnsupportedOperationException("...");
}
```

**`TestInstallUtil.addZippedTestModules()`:**

```java
// ✅ Correct — uses normalize().startsWith()
if (!zipEntryFile.toPath().normalize().startsWith(moduleRepository.toPath().normalize())) {
throw new IOException("Bad zip entry");
}
```

The fix pattern is already known and applied elsewhere in the codebase. `WebModuleUtil.startModule()` is an oversight.

### Bypass of `module.allow_web_admin`

The `module.allow_web_admin` property only restricts module operations at the Legacy UI layer (`ModuleListController`). The REST API endpoint does not consult this property:

```
Legacy UI: POST /admin/modules/moduleList.form → allowAdmin() check → [BLOCKED]
REST API: POST /ws/rest/v1/module → No allowAdmin() check → [ALLOWED]
↓
ModuleFactory.loadModule()
↓
WebModuleUtil.startModule() ← Zip Slip here, no allowAdmin check
↓
FileOutputStream.write() ← Arbitrary file write
```

## Remediation

Add `normalize().startsWith()` boundary validation before writing, consistent with the existing pattern in `ModuleUtil.expandJar()`:

```java
File outFile = new File(absPath.toString().replace("/", File.separator));

// ✅ Add this check
if (!outFile.toPath().normalize().startsWith(
Paths.get(realPath, "WEB-INF").normalize())) {
throw new UnsupportedOperationException(
"Zip entry '" + name + "' would be written outside the allowed directory.");
}
```

Additionally, enforce the `module.allow_web_admin` restriction consistently across all module upload entry points, including the REST API.