HAPI FHIR: SHCParser DEFLATE infinite loop causes denial of service

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS

• CVE-2026-81876: 0.63% estimated exploitation activity in the next 30 days; percentile 50.23 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary A malformed Smart Health Card (SHC) JWT with zip: "DEF" and an empty or truncated DEFLATE payload causes SHCParser.inflate() to loop forever. This allows an attacker who can submit SHC content for validation to pin a JVM worker thread indefinitely, causing denial of service. Details The vulnerable code is in org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/elementmodel/SHCParser.java. decodeJWT() inflates the JWT payload when the header contains "zip":"DEF": inflate() loops only on !inflater.finished() and does not check inflater.needsInput(), inflater.needsDictionary(), or zero-progress output: For empty or truncated raw DEFLATE input, Inflater.inflate() returns 0, finished() remains false, and needsInput() becomes true, producing an infinite tight loop. The same unsafe loop pattern also exists in decompress() at SHCParser.java:410-423. The validator reaches this path during SHC validation and during file-format detection for SHC-looking input (ResourceChecker.java:115-118).…

Published by the source

17 Sep 2026, 20:32 UTC

Last modified by the source

17 Sep 2026, 20:45 UTC

Source last checked

26 Oct 2026, 16:55 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-gq9c-wmrm-5hvr

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-gq9c-wmrm-5hvr

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# Patch Next advisory brief: CVE-2026-81876

Advisory: HAPI FHIR: SHCParser DEFLATE infinite loop causes denial of service
IDs: CVE-2026-81876, GHSA-gq9c-wmrm-5hvr
Record: https://patchnext.com/advisories/cve-2026-81876 (revision 2, source checked 26 Oct 2026, 16:55 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: ca.uhn.hapi.fhir:org.hl7.fhir.validation.cli 6.9.12; ca.uhn.hapi.fhir:org.hl7.fhir.validation 6.9.12; ca.uhn.hapi.fhir:org.hl7.fhir.r5 6.9.12. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven ca.uhn.hapi.fhir:org.hl7.fhir.validation.cli: affected <= 6.9.11; fixed in 6.9.12
- Maven ca.uhn.hapi.fhir:org.hl7.fhir.validation: affected <= 6.9.11; fixed in 6.9.12
- Maven ca.uhn.hapi.fhir:org.hl7.fhir.r5: affected <= 6.9.11; fixed in 6.9.12

## Suggested inspection (read-only)
- Maven ca.uhn.hapi.fhir:org.hl7.fhir.validation.cli: check the installed version with your package manager.
- Maven ca.uhn.hapi.fhir:org.hl7.fhir.validation: check the installed version with your package manager.
- Maven ca.uhn.hapi.fhir:org.hl7.fhir.r5: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on ca.uhn.hapi.fhir:org.hl7.fhir.validation.cli, ca.uhn.hapi.fhir:org.hl7.fhir.validation, ca.uhn.hapi.fhir:org.hl7.fhir.r5.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-gq9c-wmrm-5hvr (OSV record GHSA-gq9c-wmrm-5hvr lists affected ranges: Maven ca.uhn.hapi.fhir:org.hl7.fhir.r5 >=0 =0 =0 <6.9.12 (fixed))
- Verified: https://github.com/advisories/GHSA-gq9c-wmrm-5hvr (GitHub-reviewed advisory GHSA-gq9c-wmrm-5hvr lists affected ranges: Maven ca.uhn.hapi.fhir:org.hl7.fhir.r5 >=0 =0 =0 <=6.9.11)

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