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CVE-2026-81876 high CVSS 7.5

Vulnerability in ca.uhn.hapi.fhir:org.hl7.fhir.r5 (CVE-2026-81876)

Summary

Vulnerability in ca.uhn.hapi.fhir:org.hl7.fhir.r5 (CVE-2026-81876). Risk of unauthorized operations or information disclosure. Exploitable via false. Mitigation: upgrade to 6.9.12 or later.

Original description

The description as published by the source.

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":

// SHCParser.java:300-302
if ("DEF".equals(res.header.asString("zip"))) {
  payloadJson = inflate(payloadJson);
}

inflate() loops only on !inflater.finished() and does not check inflater.needsInput(), inflater.needsDictionary(), or zero-progress output:

// SHCParser.java:455-468
while (!inflater.finished()) {
  final int count = inflater.inflate(buffer);
  outputStream.write(buffer, 0, count);
}

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).

PoC

Compile the project, then run a minimal local harness that calls:

SHCParser.inflate(new byte[0]);

This never returns. Local verification:

Source: NIST National Vulnerability Database NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-81876 has been found in ca.uhn.hapi.fhir:org.hl7.fhir.r5.
Attackers can target a specific entry point like false over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: upgrade ca.uhn.hapi.fhir:org.hl7.fhir.r5 to 6.9.12 or later.
If unsure, ask your IT team or search "ca.uhn.hapi.fhir:org.hl7.fhir.r5 CVE-2026-81876" on the vendor's site.

CVE-2026-81876 (ca.uhn.hapi.fhir:org.hl7.fhir.r5) — CWE-20 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: false / true
Patched: 6.9.12 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (CWE-20) exists in ca.uhn.hapi.fhir:org.hl7.fhir.r5. Attackers reach the vulnerable code path via false without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of ca.uhn.hapi.fhir:org.hl7.fhir.r5. Attack surface: false / true.

🔥 Severity

Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 6.9.12.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Audit SBOM/dependencies to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    Audit SBOM/dependencies for affected components.

    資産台帳・SBOM・依存マニフェストで ca.uhn.hapi.fhir:org.hl7.fhir.r5 を使っているサービスとバージョンを洗い出す。

  2. 2
    Apply patch patch 
    Upgrade ca.uhn.hapi.fhir:org.hl7.fhir.r5 to 6.9.12

    ステージング環境で 6.9.12 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

maven ca.uhn.hapi.fhir:org.hl7.fhir.r5
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.9.12"}]}]
maven ca.uhn.hapi.fhir:org.hl7.fhir.validation
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.9.12"}]}]
maven ca.uhn.hapi.fhir:org.hl7.fhir.validation.cli
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.9.12"}]}]

References

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