# 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.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 16 Sep 2026
- **Updated:** 17 Sep 2026
- **Also known as:** GHSA-gq9c-wmrm-5hvr, ROOT-APP-MAVEN-CVE-2026-81876

## 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.

Weakness: CWE-835 (Loop with Unreachable Exit Condition), CWE-400 (Uncontrolled Resource Consumption), CWE-20 (Improper Input Validation)

## 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 | Ecosystem | 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.

## Is CVE-2026-81876 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-81876 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-81876 and fix it if it is affected.

What it is: 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.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-81876 exists.

Affected packages and fixed versions:
- ca.uhn.hapi.fhir:org.hl7.fhir.r5 (Maven): affected all versions; fixed in 6.9.12
- ca.uhn.hapi.fhir:org.hl7.fhir.r5 (Maven): affected all versions; fixed in 6.9.12
- ca.uhn.hapi.fhir:org.hl7.fhir.validation (Maven): affected all versions; fixed in 6.9.12
- ca.uhn.hapi.fhir:org.hl7.fhir.validation (Maven): affected all versions; fixed in 6.9.12
- ca.uhn.hapi.fhir:org.hl7.fhir.validation.cli (Maven): affected all versions; fixed in 6.9.12
- ca.uhn.hapi.fhir:org.hl7.fhir.validation.cli (Maven): affected all versions; fixed in 6.9.12

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-81876/ (Markdown: https://insights.sbomify.com/CVE-2026-81876/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-81876
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-81876
- OSV: https://osv.dev/vulnerability/CVE-2026-81876

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-81876/
Summaries are generated and may contain mistakes; the official description above is the record.