GHSA-3W98-RRPR-FPRR
Vulnerability from github – Published: 2026-09-17 20:32 – Updated: 2026-09-17 20:32Summary
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 MAX_ALLOWED_SHC_LENGTH, but this only logs an error and parsing continues:
// SHCParser.java:282-284
if (jwt.length() > MAX_ALLOWED_SHC_LENGTH) {
logError(...);
}
If the header contains "zip":"DEF", the payload is inflated before JSON parsing:
// SHCParser.java:300-304
if ("DEF".equals(res.header.asString("zip"))) {
payloadJson = inflate(payloadJson);
}
res.payload = JsonParser.parseObject(FileUtilities.bytesToString(payloadJson), true);
inflate() accumulates all decompressed output in a ByteArrayOutputStream and has no maximum output size:
// SHCParser.java:455-468
while (!inflater.finished()) {
final int count = inflater.inflate(buffer);
outputStream.write(buffer, 0, count);
}
return outputStream.toByteArray();
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 verification measured the following expansion through SHCParser.inflate():
plain=1000066 compressed=1052 inflated=1000066 ratio=950
plain=16000066 compressed=15626 inflated=16000066 ratio=1023
A small compressed payload can therefore allocate many megabytes of heap. Larger payloads can trigger OutOfMemoryError or process instability.
Impact
This is a denial-of-service vulnerability. Any validator service or application that accepts attacker-supplied SHC content can be forced to allocate excessive heap memory. Impact ranges from request failure and severe GC pressure to process termination.
Credits
- Thai Son Dinh from VinSOC Labs (R&D)
{
"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"
}
]
},
{
"package": {
"ecosystem": "Maven",
"name": "ca.uhn.hapi.fhir:org.hl7.fhir.validation.cli"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"last_affected": "5.0.0"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-81875"
],
"database_specific": {
"cwe_ids": [
"CWE-20",
"CWE-400",
"CWE-409"
],
"github_reviewed": true,
"github_reviewed_at": "2026-09-17T20:32:16Z",
"nvd_published_at": "2026-09-16T19:17:44Z",
"severity": "HIGH"
},
"details": "### Summary\n`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.\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()` checks `MAX_ALLOWED_SHC_LENGTH`, but this only logs an error and parsing continues:\n\n```java\n// SHCParser.java:282-284\nif (jwt.length() \u003e MAX_ALLOWED_SHC_LENGTH) {\n logError(...);\n}\n```\n\nIf the header contains `\"zip\":\"DEF\"`, the payload is inflated before JSON parsing:\n\n```java\n// SHCParser.java:300-304\nif (\"DEF\".equals(res.header.asString(\"zip\"))) {\n payloadJson = inflate(payloadJson);\n}\nres.payload = JsonParser.parseObject(FileUtilities.bytesToString(payloadJson), true);\n```\n\n`inflate()` accumulates all decompressed output in a `ByteArrayOutputStream` and has no maximum output size:\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}\nreturn outputStream.toByteArray();\n```\n\nThe same unbounded decompression pattern exists in `decompress()` at `SHCParser.java:410-423`.\n\n### PoC\nCreate 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\"}`.\n\nLocal verification measured the following expansion through `SHCParser.inflate()`:\n\n```text\nplain=1000066 compressed=1052 inflated=1000066 ratio=950\nplain=16000066 compressed=15626 inflated=16000066 ratio=1023\n```\n\nA small compressed payload can therefore allocate many megabytes of heap. Larger payloads can trigger `OutOfMemoryError` or process instability.\n\n### Impact\nThis is a denial-of-service vulnerability. Any validator service or application that accepts attacker-supplied SHC content can be forced to allocate excessive heap memory. Impact ranges from request failure and severe GC pressure to process termination.\n\n### Credits\n- Thai Son Dinh from VinSOC Labs (R\u0026D)",
"id": "GHSA-3w98-rrpr-fprr",
"modified": "2026-09-17T20:32:16Z",
"published": "2026-09-17T20:32:16Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/hapifhir/org.hl7.fhir.core/security/advisories/GHSA-3w98-rrpr-fprr"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-81875"
},
{
"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/fbb94216e0ad21ded75be77e5e20242ba194e83f"
},
{
"type": "PACKAGE",
"url": "https://github.com/hapifhir/org.hl7.fhir.core"
},
{
"type": "WEB",
"url": "https://github.com/hapifhir/org.hl7.fhir.core/releases/tag/6.9.11"
},
{
"type": "WEB",
"url": "https://github.com/hapifhir/org.hl7.fhir.core/releases/tag/6.9.12"
}
],
"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 unbounded DEFLATE decompression causes denial of service"
}
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
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- 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.
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