Vulnerability-Lookup

CVE-2026-81876 (GCVE-0-2026-81876)

Vulnerability from cvelistv5 – Published: 2026-09-16 18:48 – Updated: 2026-09-17 14:02

Title

HAPI FHIR: SHCParser DEFLATE infinite loop causes denial of service

Summary

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.

Severity

7.5 (High)


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

SSVC

Exploitation: poc Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-17 14:02 UTC

CWE

CWE-20 - Improper Input Validation
CWE-400 - Uncontrolled Resource Consumption
CWE-835 - Loop with Unreachable Exit Condition ('Infinite Loop')

Assigner

GitHub_M mitre root

References

4 references

URL	Tags
https://github.com/hapifhir/org.hl7.fhir.core/sec…	x_refsource_CONFIRM
https://github.com/hapifhir/org.hl7.fhir.core/pull/2493	x_refsource_MISC
https://github.com/hapifhir/org.hl7.fhir.core/com…	x_refsource_MISC
https://github.com/hapifhir/org.hl7.fhir.core/com…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
hapifhir	org.hl7.fhir.core	Affected: < 6.9.12	guessed

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-81876

Vulnerability from fkie_nvd - Published: 2026-09-16 19:17 - Updated: 2026-09-17 14:17

Severity

7.5 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/hapifhir/org.hl7.fhir.core/commit/d804558bd77372b1629e55a5b901cad3f5134cdc
	security-advisories@github.com	https://github.com/hapifhir/org.hl7.fhir.core/commit/edd5d8c139e669e39270785f08be7b63aefef24c
	security-advisories@github.com	https://github.com/hapifhir/org.hl7.fhir.core/pull/2493
	security-advisories@github.com	https://github.com/hapifhir/org.hl7.fhir.core/security/advisories/GHSA-gq9c-wmrm-5hvr
	134c704f-9b21-4f2e-91b3-4a467353bcc0	https://github.com/hapifhir/org.hl7.fhir.core/security/advisories/GHSA-gq9c-wmrm-5hvr

Impacted products

	Vendor	Product	Version

JSON

To clipboard

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          "product": "org.hl7.fhir.core",
          "vendor": "hapifhir",
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  "lastModified": "2026-09-17T14:17:32.600",
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    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/hapifhir/org.hl7.fhir.core/security/advisories/GHSA-gq9c-wmrm-5hvr"
    },
    {
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "url": "https://github.com/hapifhir/org.hl7.fhir.core/security/advisories/GHSA-gq9c-wmrm-5hvr"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Received",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-20"
        },
        {
          "lang": "en",
          "value": "CWE-400"
        },
        {
          "lang": "en",
          "value": "CWE-835"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}

GHSA-GQ9C-WMRM-5HVR

Vulnerability from github – Published: 2026-09-17 20:32 – Updated: 2026-09-17 20:32

Summary

HAPI FHIR: SHCParser DEFLATE infinite loop causes denial of service

Details

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:

timeout 3s java -cp ... VerifyDoSFindings shcHang
echo $?
# 124 = timeout killed the hung process

A JWT PoC uses:

header: Base64URL({"zip":"DEF"})
payload: empty or truncated raw DEFLATE bytes
signature: arbitrary

Submit the resulting token as SHC content, for example via a .shc file or content beginning with shc:/ that reaches the validator's SHC detection path.

Impact

This is a denial-of-service vulnerability. A single malformed SHC validation request can consume a worker thread indefinitely. In services that validate uploaded SHC content, a small number of concurrent malformed requests can exhaust all validation workers.

Credits

Thai Son Dinh from VinSOC Labs (R&D)

Severity

7.5 (High)


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

Show details on source website

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{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 6.9.11"
      },
      "package": {
        "ecosystem": "Maven",
        "name": "ca.uhn.hapi.fhir:org.hl7.fhir.r5"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.9.12"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 6.9.11"
      },
      "package": {
        "ecosystem": "Maven",
        "name": "ca.uhn.hapi.fhir:org.hl7.fhir.validation"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.9.12"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 6.9.11"
      },
      "package": {
        "ecosystem": "Maven",
        "name": "ca.uhn.hapi.fhir:org.hl7.fhir.validation.cli"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.9.12"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-81876"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-20",
      "CWE-400",
      "CWE-835"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-17T20:32:21Z",
    "nvd_published_at": "2026-09-16T19:17:44Z",
    "severity": "HIGH"
  },
  "details": "### Summary\nA 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.\n\n### Details\nThe vulnerable code is in `org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/elementmodel/SHCParser.java`.\n\n`decodeJWT()` inflates the JWT payload when the header contains `\"zip\":\"DEF\"`:\n\n```java\n// SHCParser.java:300-302\nif (\"DEF\".equals(res.header.asString(\"zip\"))) {\n  payloadJson = inflate(payloadJson);\n}\n```\n\n`inflate()` loops only on `!inflater.finished()` and does not check `inflater.needsInput()`, `inflater.needsDictionary()`, or zero-progress output:\n\n```java\n// SHCParser.java:455-468\nwhile (!inflater.finished()) {\n  final int count = inflater.inflate(buffer);\n  outputStream.write(buffer, 0, count);\n}\n```\n\nFor 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`.\n\nThe validator reaches this path during SHC validation and during file-format detection for SHC-looking input (`ResourceChecker.java:115-118`).\n\n### PoC\nCompile the project, then run a minimal local harness that calls:\n\n```java\nSHCParser.inflate(new byte[0]);\n```\n\nThis never returns. Local verification:\n\n```bash\ntimeout 3s java -cp ... VerifyDoSFindings shcHang\necho $?\n# 124 = timeout killed the hung process\n```\n\nA JWT PoC uses:\n\n- header: Base64URL(`{\"zip\":\"DEF\"}`)\n- payload: empty or truncated raw DEFLATE bytes\n- signature: arbitrary\n\nSubmit the resulting token as SHC content, for example via a `.shc` file or content beginning with `shc:/` that reaches the validator\u0027s SHC detection path.\n\n### Impact\nThis is a denial-of-service vulnerability. A single malformed SHC validation request can consume a worker thread indefinitely. In services that validate uploaded SHC content, a small number of concurrent malformed requests can exhaust all validation workers.\n\n### Credits\n- Thai Son Dinh from VinSOC Labs (R\u0026D)",
  "id": "GHSA-gq9c-wmrm-5hvr",
  "modified": "2026-09-17T20:32:21Z",
  "published": "2026-09-17T20:32:21Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/hapifhir/org.hl7.fhir.core/security/advisories/GHSA-gq9c-wmrm-5hvr"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-81876"
    },
    {
      "type": "WEB",
      "url": "https://github.com/hapifhir/org.hl7.fhir.core/pull/2493"
    },
    {
      "type": "WEB",
      "url": "https://github.com/hapifhir/org.hl7.fhir.core/commit/d804558bd77372b1629e55a5b901cad3f5134cdc"
    },
    {
      "type": "WEB",
      "url": "https://github.com/hapifhir/org.hl7.fhir.core/commit/edd5d8c139e669e39270785f08be7b63aefef24c"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/hapifhir/org.hl7.fhir.core"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "HAPI FHIR: SHCParser DEFLATE infinite loop causes denial of service"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

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Action not permitted

CVE-2026-81876 (GCVE-0-2026-81876)

FKIE_CVE-2026-81876

GHSA-GQ9C-WMRM-5HVR

Summary

Details

PoC

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Credits

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