CVE-2026-45367

HAPI FHIR: ReDoS via FHIRPath matches()/replaceMatches() in FHIR Validator HTTP Endpoint

private List<Base> funcMatches(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    String sw = convertToString(swb); // attacker-controlled regex pattern
    // ...
    Pattern p = Pattern.compile("(?s)" + sw); // VULNERABLE: no complexity check
    Matcher m = p.matcher(st);                // no timeout
    boolean ok = m.find();

Pattern p = Pattern.compile("(?s)" + sw); // VULNERABLE: same pattern
Matcher m = p.matcher(st);
boolean ok = m.matches();

result.add(new StringType(convertToString(focus.get(0))
    .replaceAll(regex, repl)).noExtensions()); // VULNERABLE: replaceAll uses Pattern internally

• CPU Exhaustion: The exponential backtracking in Java's regex engine consumes 100% of a CPU core for the duration of the hang (effectively infinite for sufficiently long input strings) for callers of FHIRPathEngine.

A regular expression with worst-case exponential or polynomial matching time is applied to untrusted input, causing excessive CPU use. Typical impact: denial of service when input is crafted to trigger backtracking.

CVE-2026-45367 has a CVSS score of 7.5 (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 (6.9.7); upgrading removes the vulnerable code path.

Kodem intelligence

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1. What is CVE-2026-45367? CVE-2026-45367 is a high-severity inefficient regular expression (ReDoS) vulnerability in ca.uhn.hapi.fhir:org.hl7.fhir.dstu2 (maven), affecting versions <= 6.9.6. It is fixed in 6.9.7. A regular expression with worst-case exponential or polynomial matching time is applied to untrusted input, causing excessive CPU use.
2. How severe is CVE-2026-45367? CVE-2026-45367 has a CVSS score of 7.5 (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-2026-45367?
   • ca.uhn.hapi.fhir:org.hl7.fhir.dstu2 (maven) (versions <= 6.9.6)
   • ca.uhn.hapi.fhir:org.hl7.fhir.dstu2016may (maven) (versions <= 6.9.6)
   • ca.uhn.hapi.fhir:org.hl7.fhir.dstu3 (maven) (versions <= 6.9.6)
   • ca.uhn.hapi.fhir:org.hl7.fhir.r4 (maven) (versions <= 6.9.6)
   • ca.uhn.hapi.fhir:org.hl7.fhir.r4b (maven) (versions <= 6.9.6)
   • ca.uhn.hapi.fhir:org.hl7.fhir.r5 (maven) (versions <= 6.9.6)
   • ca.uhn.hapi.fhir:org.hl7.fhir.validation (maven) (versions <= 6.9.6)
   • ca.uhn.hapi.fhir:org.hl7.fhir.validation.cli (maven) (versions <= 6.9.6)
4. Is there a fix for CVE-2026-45367? Yes. CVE-2026-45367 is fixed in 6.9.7. Upgrade to this version or later.
5. Is CVE-2026-45367 exploitable, and should I be worried? Whether CVE-2026-45367 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-2026-45367 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-2026-45367?
   • Upgrade ca.uhn.hapi.fhir:org.hl7.fhir.dstu2 to 6.9.7 or later
   • Upgrade ca.uhn.hapi.fhir:org.hl7.fhir.dstu2016may to 6.9.7 or later
   • Upgrade ca.uhn.hapi.fhir:org.hl7.fhir.dstu3 to 6.9.7 or later
   • Upgrade ca.uhn.hapi.fhir:org.hl7.fhir.r4 to 6.9.7 or later
   • Upgrade ca.uhn.hapi.fhir:org.hl7.fhir.r4b to 6.9.7 or later
   • Upgrade ca.uhn.hapi.fhir:org.hl7.fhir.r5 to 6.9.7 or later
   • Upgrade ca.uhn.hapi.fhir:org.hl7.fhir.validation to 6.9.7 or later
   • Upgrade ca.uhn.hapi.fhir:org.hl7.fhir.validation.cli to 6.9.7 or later

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