{"id":"CVE-2026-40076","aliases":["GHSA-78fc-9688-w8xw"],"url":"https://o3.security/vulnerability/CVE-2026-40076","summary":"OpenMRS Core arbitrary file write and code execution via Zip Slip in module upload","details":"## Affected Versions\n\nversion ≤ 2.7.8 (latest version at time of disclosure)\n\nhttps://github.com/openmrs/openmrs-core\n\n## Impact\n\nThe 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.\n\nNotably, 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.\n\nFurthermore, 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.\n\n## Steps to Reproduce\n\n1. 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/../../../../`. Upload this file to `POST /openmrs/ws/rest/v1/module` with valid admin credentials via Basic Auth.\n\n\"image\"\n\n\"image\"\n\n\n2. 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/`.\n\n\"image\"\n\n3. 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.\n\n\"image\"\n\n## Root Cause Analysis\n\nThe vulnerability exists in `WebModuleUtil.startModule()` (`web/src/main/java/org/openmrs/module/web/WebModuleUtil.java`).\n\n### Vulnerable code:\n\n```java\nEnumeration entries = jarFile.entries();\nwhile (entries.hasMoreElements()) {\n JarEntry entry = entries.nextElement();\n String name = entry.getName();\n\n // ❌ Incomplete check — only blocks entries starting with \"..\"\n if (Paths.get(name).startsWith(\"..\")) {\n throw new UnsupportedOperationException(\"...\");\n }\n\n if (name.startsWith(\"web/module/\")) {\n String filepath = name.substring(11);\n StringBuilder absPath = new StringBuilder(realPath + \"/WEB-INF\");\n absPath.append(\"/view/module/\");\n absPath.append(mod.getModuleIdAsPath()).append(\"/\").append(filepath);\n\n // ❌ No normalize() or startsWith() boundary check before writing\n File outFile = new File(absPath.toString().replace(\"/\", File.separator));\n outStream = new FileOutputStream(outFile, false);\n inStream = jarFile.getInputStream(entry);\n OpenmrsUtil.copyFile(inStream, outStream);\n }\n}\n```\n\n**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.\n\n### Correctly protected code in the same codebase:\n\n**`ModuleUtil.expandJar()`:**\n\n```java\n// ✅ Correct — uses normalize().startsWith()\nif (!parent.toPath().normalize().startsWith(docBase)) {\n throw new UnsupportedOperationException(\"...\");\n}\n```\n\n**`TestInstallUtil.addZippedTestModules()`:**\n\n```java\n// ✅ Correct — uses normalize().startsWith()\nif (!zipEntryFile.toPath().normalize().startsWith(moduleRepository.toPath().normalize())) {\n throw new IOException(\"Bad zip entry\");\n}\n```\n\nThe fix pattern is already known and applied elsewhere in the codebase. `WebModuleUtil.startModule()` is an oversight.\n\n### Bypass of `module.allow_web_admin`\n\nThe `module.allow_web_admin` property only restricts module operations at the Legacy UI layer (`ModuleListController`). The REST API endpoint does not consult this property:\n\n```\nLegacy UI: POST /admin/modules/moduleList.form → allowAdmin() check → [BLOCKED]\nREST API: POST /ws/rest/v1/module → No allowAdmin() check → [ALLOWED]\n ↓\n ModuleFactory.loadModule()\n ↓\n WebModuleUtil.startModule() ← Zip Slip here, no allowAdmin check\n ↓\n FileOutputStream.write() ← Arbitrary file write\n```\n\n## Remediation\n\nAdd `normalize().startsWith()` boundary validation before writing, consistent with the existing pattern in `ModuleUtil.expandJar()`:\n\n```java\nFile outFile = new File(absPath.toString().replace(\"/\", File.separator));\n\n// ✅ Add this check\nif (!outFile.toPath().normalize().startsWith(\n Paths.get(realPath, \"WEB-INF\").normalize())) {\n throw new UnsupportedOperationException(\n \"Zip entry '\" + name + \"' would be written outside the allowed directory.\");\n}\n```\n\nAdditionally, enforce the `module.allow_web_admin` restriction consistently across all module upload entry points, including the REST API.","published":"2026-05-06T19:32:13.851Z","modified":"2026-08-12T03:51:08.748516814Z","cvss":null,"epss":{"score":0.00853,"percentile":0.55098,"asOf":"2026-08-14"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Maven","name":"org.openmrs.web:openmrs-web","fixedVersion":null},{"ecosystem":"Maven","name":"org.openmrs.web:openmrs-web","fixedVersion":null}],"fix":null,"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/40xxx/CVE-2026-40076.json"},{"type":"ADVISORY","url":"https://github.com/openmrs/openmrs-core/security/advisories/GHSA-78fc-9688-w8xw"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-40076"},{"type":"PACKAGE","url":"https://github.com/openmrs/openmrs-core"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:08.748516814Z"}}