CVE-2026-81876 HAPI FHIR: SHCParser DEFLATE infinite loop causes denial of service
Attackers can cause a denial of service in HAPI FHIR by sending malformed Smart Health Card JWTs that trigger an infinite loop in the parser.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-81876?
CVE-2026-81876 is a high-severity denial of service vulnerability in hapifhir org.hl7.fhir.core, published on 16 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
HAPI FHIR is a complete implementation of the HL7 FHIR standard for healthcare interoperability in Java. Prior to version 6.9.12, SHCParser in org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/elementmodel/SHCParser.java can enter an infinite loop while processing attacker-controlled Smart Health Card JWT content whose header contains zip: "DEF" and whose raw-DEFLATE payload is empty or truncated. SHCParser.decodeJWT() reaches SHCParser.inflate(), where Inflater.inflate() can return zero while Inflater.finished() remains false and Inflater.needsInput() is true. The loop also lacks an Inflater.needsDictionary() termination check, SHCParser.decompress() contains the same zero-progress pattern, and ResourceChecker.java can reach SHC parsing during file-format detection. A malformed validation request can pin a JVM worker thread indefinitely, and concurrent requests can exhaust all validation workers. This issue is fixed in version 6.9.12.
Which versions are affected by CVE-2026-81876?
6 open source packages ship an affected version, including ca.uhn.hapi.fhir:org.hl7.fhir.r5, ca.uhn.hapi.fhir:org.hl7.fhir.validation and ca.uhn.hapi.fhir:org.hl7.fhir.validation.cli.
| Package | Affected | Fixed in |
|---|---|---|
ca.uhn.hapi.fhir:org.hl7.fhir.r5 Maven | All versions | 6.9.12 |
ca.uhn.hapi.fhir:org.hl7.fhir.r5 Maven | All versions | 6.9.12 |
ca.uhn.hapi.fhir:org.hl7.fhir.validation Maven | All versions | 6.9.12 |
ca.uhn.hapi.fhir:org.hl7.fhir.validation Maven | All versions | 6.9.12 |
ca.uhn.hapi.fhir:org.hl7.fhir.validation.cli Maven | All versions | 6.9.12 |
ca.uhn.hapi.fhir:org.hl7.fhir.validation.cli Maven | All versions | 6.9.12 |
How do I fix CVE-2026-81876?
Upgrade ca.uhn.hapi.fhir:org.hl7.fhir.r5 to 6.9.12 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-81876 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-81876 exists.
Sources
Also known as GHSA-gq9c-wmrm-5hvr, ROOT-APP-MAVEN-CVE-2026-81876.