Summary
org.hl7.fhir.core: ReDoS via FHIRPath matches()/replaceMatches() in FHIR Validator HTTP Endpoint
Full technical description
All implementations of FHIRPathEngine accept arbitrary FHIRPath expressions and evaluate them without input validation. The utility intended to secure this evaluation did so incorrectly, and did not fully cover all places in which evaluation was being done. An attacker can send a resource containing an evil regex pattern that causes catastrophic backtracking, exhausting system resources, and causing Denial-of-Service.
Details
The vulnerability exists in regex execution in FHIRPathEngine implementations across multiple code modules. The FHIRPath functions matches(), matchesFull(), and replaceMatches() pass user-controlled regular expressions to Java's Pattern.compile() and String.replaceAll() through a utility class designed to time out after a specified interval. That utility correctly cancelled a single executor thread and returned with an exception, but the execution within the thread had no means to listen for this cancellation and would persist. Furthermore, three modules contained method calls in FHIRPathEngine that were not protected by this utility class.
Why this is exploitable:
Java's Pattern.compile() with a pattern like (a+)+$ against input "aaaaaaaaaaaaaaaaaaaaaa!" causes exponential backtracking (O(2^n) time complexity).
Impact
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.
Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.
CVE-2026-49485 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 (6.9.9, 6.9.4.2); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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ca.uhn.hapi.fhir:org.hl7.fhir.dstu2 to 6.9.9 or later; ca.uhn.hapi.fhir:org.hl7.fhir.dstu2016may to 6.9.9 or later; ca.uhn.hapi.fhir:org.hl7.fhir.dstu3 to 6.9.9 or later; ca.uhn.hapi.fhir:org.hl7.fhir.r4 to 6.9.9 or later; ca.uhn.hapi.fhir:org.hl7.fhir.r4b to 6.9.9 or later; ca.uhn.hapi.fhir:org.hl7.fhir.r5 to 6.9.9 or later; ca.uhn.hapi.fhir:org.hl7.fhir.validation to 6.9.9 or later; ca.uhn.hapi.fhir:org.hl7.fhir.validation.cli to 6.9.9 or later; ca.uhn.hapi.fhir:org.hl7.fhir.dstu2 to 6.9.4.2 or later; ca.uhn.hapi.fhir:org.hl7.fhir.dstu2016may to 6.9.4.2 or later; ca.uhn.hapi.fhir:org.hl7.fhir.dstu3 to 6.9.4.2 or later; ca.uhn.hapi.fhir:org.hl7.fhir.r4 to 6.9.4.2 or later; ca.uhn.hapi.fhir:org.hl7.fhir.r4b to 6.9.4.2 or later; ca.uhn.hapi.fhir:org.hl7.fhir.r5 to 6.9.4.2 or later; ca.uhn.hapi.fhir:org.hl7.fhir.validation to 6.9.4.2 or later; ca.uhn.hapi.fhir:org.hl7.fhir.validation.cli to 6.9.4.2 or later
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2026-49485? CVE-2026-49485 is a high-severity uncontrolled resource consumption vulnerability in ca.uhn.hapi.fhir:org.hl7.fhir.dstu2 (maven), affecting versions >= 6.9.5, < 6.9.9. It is fixed in 6.9.9, 6.9.4.2. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
- How severe is CVE-2026-49485? CVE-2026-49485 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.
- Which packages are affected by CVE-2026-49485?
ca.uhn.hapi.fhir:org.hl7.fhir.dstu2(maven) (versions >= 6.9.5, < 6.9.9)ca.uhn.hapi.fhir:org.hl7.fhir.dstu2016may(maven) (versions >= 6.9.5, < 6.9.9)ca.uhn.hapi.fhir:org.hl7.fhir.dstu3(maven) (versions >= 6.9.5, < 6.9.9)ca.uhn.hapi.fhir:org.hl7.fhir.r4(maven) (versions >= 6.9.5, < 6.9.9)ca.uhn.hapi.fhir:org.hl7.fhir.r4b(maven) (versions >= 6.9.5, < 6.9.9)ca.uhn.hapi.fhir:org.hl7.fhir.r5(maven) (versions >= 6.9.5, < 6.9.9)ca.uhn.hapi.fhir:org.hl7.fhir.validation(maven) (versions >= 6.9.5, < 6.9.9)ca.uhn.hapi.fhir:org.hl7.fhir.validation.cli(maven) (versions >= 6.9.5, < 6.9.9)
- Is there a fix for CVE-2026-49485? Yes. CVE-2026-49485 is fixed in 6.9.9, 6.9.4.2. Upgrade to this version or later.
- Is CVE-2026-49485 exploitable, and should I be worried? Whether CVE-2026-49485 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
- What actually determines whether CVE-2026-49485 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.
- How do I fix CVE-2026-49485?
- Upgrade
ca.uhn.hapi.fhir:org.hl7.fhir.dstu2to 6.9.9 or later - Upgrade
ca.uhn.hapi.fhir:org.hl7.fhir.dstu2016mayto 6.9.9 or later - Upgrade
ca.uhn.hapi.fhir:org.hl7.fhir.dstu3to 6.9.9 or later - Upgrade
ca.uhn.hapi.fhir:org.hl7.fhir.r4to 6.9.9 or later - Upgrade
ca.uhn.hapi.fhir:org.hl7.fhir.r4bto 6.9.9 or later - Upgrade
ca.uhn.hapi.fhir:org.hl7.fhir.r5to 6.9.9 or later - Upgrade
ca.uhn.hapi.fhir:org.hl7.fhir.validationto 6.9.9 or later - Upgrade
ca.uhn.hapi.fhir:org.hl7.fhir.validation.clito 6.9.9 or later - Upgrade
ca.uhn.hapi.fhir:org.hl7.fhir.dstu2to 6.9.4.2 or later - Upgrade
ca.uhn.hapi.fhir:org.hl7.fhir.dstu2016mayto 6.9.4.2 or later - Upgrade
ca.uhn.hapi.fhir:org.hl7.fhir.dstu3to 6.9.4.2 or later - Upgrade
ca.uhn.hapi.fhir:org.hl7.fhir.r4to 6.9.4.2 or later - Upgrade
ca.uhn.hapi.fhir:org.hl7.fhir.r4bto 6.9.4.2 or later - Upgrade
ca.uhn.hapi.fhir:org.hl7.fhir.r5to 6.9.4.2 or later - Upgrade
ca.uhn.hapi.fhir:org.hl7.fhir.validationto 6.9.4.2 or later - Upgrade
ca.uhn.hapi.fhir:org.hl7.fhir.validation.clito 6.9.4.2 or later
- Upgrade