Vulnerability · Published Sep 16, 2026 · Assigned by GitHub_M

CVE-2026-81876HAPI FHIR: SHCParser DEFLATE infinite loop causes denial of service

High 7.5

In plain English

A high-severity improper input validation in org.hl7.fhir.core from hapifhir. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 50% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.5High

Exploit odds (30 days)0.6%top 49.6% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Maven	ca.uhn.hapi.fhir:org.hl7.fhir.r5	6.9.12	GHSA-gq9c-wmrm-5hvr
Maven	ca.uhn.hapi.fhir:org.hl7.fhir.validation	6.9.12	GHSA-gq9c-wmrm-5hvr
Maven	ca.uhn.hapi.fhir:org.hl7.fhir.validation.cli	6.9.12	GHSA-gq9c-wmrm-5hvr

Affected products (as reported)

Vendor	Product	Versions
hapifhir	org.hl7.fhir.core	< 6.9.12

Weakness: CWE-20, CWE-400, CWE-835 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

https://github.com/hapifhir/org.hl7.fhir.core/security/advisories/GHSA-gq9c-wmrm-5hvr x_refsource_CONFIRM
https://github.com/hapifhir/org.hl7.fhir.core/pull/2493 x_refsource_MISC
https://github.com/hapifhir/org.hl7.fhir.core/commit/d804558bd77372b1629e55a5b901cad3f5134cdc x_refsource_MISC
https://github.com/hapifhir/org.hl7.fhir.core/commit/edd5d8c139e669e39270785f08be7b63aefef24c x_refsource_MISC