CVE-2021-32769 is a high-severity (CVSS 7.5) Path Traversal vulnerability in io.micronaut:micronaut-http-server-netty. 1 public exploit reference exists, so weaponization risk is real. A fix is available for io.micronaut:micronaut-http-server-netty — see the affected versions and patch details below.
Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') in micronaut-core
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2021-32769 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,636 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
io.micronaut:micronaut-http-server-nettyReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.
Description
With a basic configuration like
router:
static-resources:
assets:
enabled: true
mapping: /.assets/public/**
paths: file:/home/lstrmiska/test/
it is possible to access any file from a filesystem, using "/../../" in URL, as Micronaut does not restrict file access to configured paths.
Repro Steps
- create a file test.txt in /home/lstrmiska
- start micronaut
- execute command
curl -v --path-as-is "http://localhost:8080/.assets/public/../test.txt"
Impact
Micronaut can potentially leak sensitive information.
See https://cwe.mitre.org/data/definitions/22.html
Patches
diff --git a/core/src/main/java/io/micronaut/core/io/file/DefaultFileSystemResourceLoader.java b/core/src/main/java/io/micronaut/core/io/file/DefaultFileSystemResourceLoader.java
index 2f5a91403..19d3b7f05 100644
--- a/core/src/main/java/io/micronaut/core/io/file/DefaultFileSystemResourceLoader.java
+++ b/core/src/main/java/io/micronaut/core/io/file/DefaultFileSystemResourceLoader.java
@@ -69,6 +69,9 @@ public class DefaultFileSystemResourceLoader implements FileSystemResourceLoader
@Override
public Optional<InputStream> getResourceAsStream(String path) {
Path filePath = getFilePath(normalize(path));
+ if (pathOutsideBase(filePath)) {
+ return Optional.empty();
+ }
try {
return Optional.of(Files.newInputStream(filePath));
} catch (IOException e) {
@@ -79,7 +82,7 @@ public class DefaultFileSystemResourceLoader implements FileSystemResourceLoader
@Override
public Optional<URL> getResource(String path) {
Path filePath = getFilePath(normalize(path));
- if (Files.exists(filePath) && Files.isReadable(filePath) && !Files.isDirectory(filePath)) {
+ if (!pathOutsideBase(filePath) && Files.exists(filePath) && Files.isReadable(filePath) && !Files.isDirectory(filePath)) {
try {
URL url = filePath.toUri().toURL();
return Optional.of(url);
@@ -117,4 +120,15 @@ public class DefaultFileSystemResourceLoader implements FileSystemResourceLoader
private Path getFilePath(String path) {
return baseDirPath.map(dir -> dir.resolve(path)).orElseGet(() -> Paths.get(path));
}
+
+ private boolean pathOutsideBase(Path path) {
+ if (baseDirPath.isPresent()) {
+ Path baseDir = baseDirPath.get();
+ if (path.isAbsolute() == baseDir.isAbsolute()) {
+ Path relativePath = baseDir.relativize(path);
+ return relativePath.startsWith("..");
+ }
+ }
+ return false;
+ }
}
--
Workarounds
- do not use ** in mapping, use only * which exposes only flat structure of a directory not allowing traversal
- run micronaut in chroot (linux only)
References
See https://cwe.mitre.org/data/definitions/22.html
For more information
If you have any questions or comments about this advisory:
- Open an issue in Github
- Email us at [email protected]
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | io.micronaut:micronaut-http-server-netty | all versions | 2.5.9io.micronaut:micronaut-http-server-netty:2.5.9 |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for io.micronaut:micronaut-http-server-netty, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update io.micronaut:micronaut-http-server-netty to 2.5.9 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-32769 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 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2021-32769 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2021-32769. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2021-32769 in your dependencies?
O3 Security finds CVE-2021-32769 across Maven dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.