HAPI FHIR: SHCParser unbounded DEFLATE decompression 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-2026-81875: 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 SHCParser inflates compressed Smart Health Card JWT payloads into memory without a decompressed-size limit. An attacker who can submit SHC content for validation can craft a small compressed JWT payload that expands to a very large byte array, causing memory exhaustion or severe garbage collection pressure. Details The vulnerable code is in org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/elementmodel/SHCParser.java. decodeJWT() checks MAXALLOWEDSHCLENGTH, but this only logs an error and parsing continues: If the header contains "zip":"DEF", the payload is inflated before JSON parsing: inflate() accumulates all decompressed output in a ByteArrayOutputStream and has no maximum output size: The same unbounded decompression pattern exists in decompress() at SHCParser.java:410-423. PoC Create a highly compressible SHC-shaped JSON payload, compress it with raw DEFLATE (new Deflater(9, true)), Base64URL-encode it as the JWT payload, and set the JWT header to {"zip":"DEF"}. Local…

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-3w98-rrpr-fprr

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-3w98-rrpr-fprr

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-81875

Advisory: HAPI FHIR: SHCParser unbounded DEFLATE decompression causes denial of service
IDs: CVE-2026-81875, GHSA-3w98-rrpr-fprr
Record: https://patchnext.com/advisories/cve-2026-81875 (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: Partial vendor fix; fixed versions by package: 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 <= 5.0.0
- 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
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## 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-3w98-rrpr-fprr (OSV record GHSA-3w98-rrpr-fprr lists affected ranges: Maven ca.uhn.hapi.fhir:org.hl7.fhir.r5 >=0 =0 =0 <=5.0.0)
- Verified: https://github.com/advisories/GHSA-3w98-rrpr-fprr (GitHub-reviewed advisory GHSA-3w98-rrpr-fprr lists affected ranges: Maven ca.uhn.hapi.fhir:org.hl7.fhir.r5 >=0 =0 =0 <=5.0.0)

Commands are suggestions: review each one before running it.