Vulnerability-Lookup

CVE-2026-55470 (GCVE-0-2026-55470)

Vulnerability from cvelistv5 – Published: 2026-07-08 21:27 – Updated: 2026-07-09 12:59

Title

HAPI FHIR: DSTU2 FHIRPathEngine.matches() missing RegexTimeout protection allows ReDoS

Summary

HAPI FHIR is a complete implementation of the HL7 FHIR standard for healthcare interoperability in Java. Prior to 6.9.10, the fix for CVE-2026-45367 incompletely patched the DSTU2 module, leaving FHIRPathEngine.matches() in org.hl7.fhir.dstu2/utils/FHIRPathEngine.java to call raw String.matches(sw) without RegexTimeout protection while replaceMatches() was updated, allowing an unauthenticated attacker to trigger catastrophic regex backtracking and exhaust server CPU. This issue is fixed in version 6.9.10.

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 (v2.0.3)

CWE

CWE-1333 - Inefficient Regular Expression Complexity

Assigner

GitHub_M

References

3 references

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

Impacted products

1 product

Vendor	Product	Version
hapifhir	org.hl7.fhir.core	Affected: < 6.9.10

Show details on NVD website

JSON

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FKIE_CVE-2026-55470

Vulnerability from fkie_nvd - Published: 2026-07-08 22:17 - Updated: 2026-07-16 16:31

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/56376f7986222626af061ca7fc27ee1ab030e590	Patch
security-advisories@github.com	https://github.com/hapifhir/org.hl7.fhir.core/releases/tag/6.9.10	Release Notes
security-advisories@github.com	https://github.com/hapifhir/org.hl7.fhir.core/security/advisories/GHSA-fxj4-p9xp-37v5	Exploit, Third Party Advisory
134c704f-9b21-4f2e-91b3-4a467353bcc0	https://github.com/hapifhir/org.hl7.fhir.core/security/advisories/GHSA-fxj4-p9xp-37v5	Exploit, Third Party Advisory

Impacted products

	Vendor	Product	Version
	hapifhir	hl7_fhir_core	*

JSON

To clipboard

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      "affectedData": [
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          "product": "org.hl7.fhir.core",
          "vendor": "hapifhir",
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  "lastModified": "2026-07-16T16:31:26.300",
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GHSA-FXJ4-P9XP-37V5

Vulnerability from github – Published: 2026-06-17 18:47 – Updated: 2026-06-17 18:47

Summary

HAPI FHIR: Incomplete fix for CVE-2026-45367: DSTU2 FHIRPathEngine.matches() missing RegexTimeout protection allows ReDoS

Details

Summary

The fix for CVE-2026-45367 added RegexTimeout protection to the matches() function in DSTU2016MAY, DSTU3, R4, R4B, and R5, but the DSTU2 module was incompletely patched. In org.hl7.fhir.dstu2, replaceMatches() was updated while matches() at line 2462 still calls the raw String.matches(sw) without any timeout, allowing an unauthenticated attacker to trigger catastrophic regex backtracking and exhaust server CPU.

Details

Incomplete patch

Within the same file (org.hl7.fhir.dstu2/utils/FHIRPathEngine.java), the two functions were patched inconsistently:

Line 2226 — replaceMatches() — PATCHED:

result.add(new StringType(
    RegexTimeout.replaceAll(
        convertToString(focus.get(0)), regex, repl, regexTimeoutMillis)));

Line 2462 — matches() — NOT PATCHED:

result.add(new BooleanType(
    convertToString(focus.get(0)).matches(sw)));
// ↑ raw String.matches() — no RegexTimeout, no complexity check

DSTU3 line 2447 — matches() — PATCHED (for comparison):

result.add(new BooleanType(
    RegexTimeout.matches(st, sw, regexTimeoutMillis)));

Module-by-module status

Module	`matches()`	`replaceMatches()`
DSTU2	❌ raw `str.matches(sw)`	✅ `RegexTimeout.replaceAll()`
DSTU2016MAY	✅ `RegexTimeout.matches()`	✅
DSTU3	✅ `RegexTimeout.matches()`	✅
R4	✅ `RegexTimeout.matches()`	✅
R4B	✅ `RegexTimeout.matches()`	✅
R5	✅ `RegexTimeout.matches()`	✅

PoC

Requirements: Java 17+, Maven 3.8+

pom.xml dependencies:

<dependency>
    <groupId>ca.uhn.hapi.fhir</groupId>
    <artifactId>org.hl7.fhir.utilities</artifactId>
    <version>6.9.7</version>
</dependency>

Test code (reproduces the exact behaviour of DSTU2 line 2462):

import org.hl7.fhir.utilities.regex.RegexTimeout;
import java.util.concurrent.*;

String regex = "((a|b){0,5}){20}";
String input = "a".repeat(25) + "c";    // no match → full backtracking

// ① Patched approach — RegexTimeout terminates at 500 ms
long t1 = System.currentTimeMillis();
try {
    RegexTimeout.matches(input, regex, 500);
} catch (TimeoutException e) {
    System.out.println("RegexTimeout blocked in " +
        (System.currentTimeMillis() - t1) + " ms");
}

// ② DSTU2 line 2462 — raw String.matches(), no timeout
long t2 = System.currentTimeMillis();
input.matches(regex);                   // equivalent to what FHIRPathEngine does
System.out.println("str.matches() ran for " +
    (System.currentTimeMillis() - t2) + " ms with no timeout");

Verified output (JDK 25.0.3, Linux):

RegexTimeout blocked in 508 ms      ← patched modules: attack stopped
str.matches() ran for 1410 ms       ← DSTU2: no timeout, CPU exhausted

The patched approach cuts off the evaluation at 508 ms. The unpatched DSTU2 code runs for 1410 ms on this input with no mechanism to stop it. Longer inputs or more complex patterns produce proportionally worse results.

Impact

Vulnerability type: Regular Expression Denial of Service (ReDoS) causing CPU exhaustion and service disruption.

Who is impacted: Any application using the ca.uhn.hapi.fhir:org.hl7.fhir.dstu2 module that evaluates user-supplied FHIRPath expressions — including the FHIR Validator HTTP endpoint, FHIR servers applying FHIRPath invariants from user-provided resources or profiles, and any system embedding FHIRPathEngine from the DSTU2 module. No authentication is required; an attacker needs only to submit a FHIR resource or FHIRPath expression whose matches() argument contains a catastrophically backtracking regular expression.

Severity

7.5 (High)


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

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{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 6.9.9"
      },
      "package": {
        "ecosystem": "Maven",
        "name": "ca.uhn.hapi.fhir:org.hl7.fhir.dstu2"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.9.10"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 6.9.9"
      },
      "package": {
        "ecosystem": "Maven",
        "name": "ca.uhn.hapi.fhir:org.hl7.fhir.convertors"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.9.10"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 6.9.9"
      },
      "package": {
        "ecosystem": "Maven",
        "name": "ca.uhn.hapi.fhir:org.hl7.fhir.validation"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.9.10"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 6.9.9"
      },
      "package": {
        "ecosystem": "Maven",
        "name": "ca.uhn.hapi.fhir:org.hl7.fhir.validation.cli"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.9.10"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-55470"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-1333"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-17T18:47:23Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "## Summary\nThe fix for CVE-2026-45367 added `RegexTimeout` protection to the `matches()` function in DSTU2016MAY, DSTU3, R4, R4B, and R5, but the DSTU2 module was incompletely patched. In `org.hl7.fhir.dstu2`, `replaceMatches()` was updated while `matches()` at line 2462 still calls the raw `String.matches(sw)` without any timeout, allowing an unauthenticated attacker to trigger catastrophic regex backtracking and exhaust server CPU.\n\n\n## Details\n### Incomplete patch\n\nWithin the same file\n(`org.hl7.fhir.dstu2/utils/FHIRPathEngine.java`), the two functions were\npatched inconsistently:\n\n**Line 2226 \u2014 replaceMatches() \u2014 PATCHED:**\n```java\nresult.add(new StringType(\n    RegexTimeout.replaceAll(\n        convertToString(focus.get(0)), regex, repl, regexTimeoutMillis)));\n```\n\n**Line 2462 \u2014 matches() \u2014 NOT PATCHED:**\n```java\nresult.add(new BooleanType(\n    convertToString(focus.get(0)).matches(sw)));\n// \u2191 raw String.matches() \u2014 no RegexTimeout, no complexity check\n```\n\n**DSTU3 line 2447 \u2014 matches() \u2014 PATCHED (for comparison):**\n```java\nresult.add(new BooleanType(\n    RegexTimeout.matches(st, sw, regexTimeoutMillis)));\n```\n\n### Module-by-module status\n\n| Module | `matches()` | `replaceMatches()` |\n|---|---|---|\n| **DSTU2** | \u274c raw `str.matches(sw)` | \u2705 `RegexTimeout.replaceAll()` |\n| DSTU2016MAY | \u2705 `RegexTimeout.matches()` | \u2705 |\n| DSTU3 | \u2705 `RegexTimeout.matches()` | \u2705 |\n| R4 | \u2705 `RegexTimeout.matches()` | \u2705 |\n| R4B | \u2705 `RegexTimeout.matches()` | \u2705 |\n| R5 | \u2705 `RegexTimeout.matches()` | \u2705 |\n\n\n## PoC\n**Requirements:** Java 17+, Maven 3.8+\n\n**pom.xml dependencies:**\n```xml\n\u003cdependency\u003e\n    \u003cgroupId\u003eca.uhn.hapi.fhir\u003c/groupId\u003e\n    \u003cartifactId\u003eorg.hl7.fhir.utilities\u003c/artifactId\u003e\n    \u003cversion\u003e6.9.7\u003c/version\u003e\n\u003c/dependency\u003e\n```\n\n**Test code (reproduces the exact behaviour of DSTU2 line 2462):**\n```java\nimport org.hl7.fhir.utilities.regex.RegexTimeout;\nimport java.util.concurrent.*;\n\nString regex = \"((a|b){0,5}){20}\";\nString input = \"a\".repeat(25) + \"c\";    // no match \u2192 full backtracking\n\n// \u2460 Patched approach \u2014 RegexTimeout terminates at 500 ms\nlong t1 = System.currentTimeMillis();\ntry {\n    RegexTimeout.matches(input, regex, 500);\n} catch (TimeoutException e) {\n    System.out.println(\"RegexTimeout blocked in \" +\n        (System.currentTimeMillis() - t1) + \" ms\");\n}\n\n// \u2461 DSTU2 line 2462 \u2014 raw String.matches(), no timeout\nlong t2 = System.currentTimeMillis();\ninput.matches(regex);                   // equivalent to what FHIRPathEngine does\nSystem.out.println(\"str.matches() ran for \" +\n    (System.currentTimeMillis() - t2) + \" ms with no timeout\");\n```\n\n**Verified output (JDK 25.0.3, Linux):**\n```\nRegexTimeout blocked in 508 ms      \u2190 patched modules: attack stopped\nstr.matches() ran for 1410 ms       \u2190 DSTU2: no timeout, CPU exhausted\n```\n\nThe patched approach cuts off the evaluation at 508 ms. The unpatched DSTU2\ncode runs for 1410 ms on this input with no mechanism to stop it. Longer\ninputs or more complex patterns produce proportionally worse results.\n\n\n## Impact\n**Vulnerability type:** Regular Expression Denial of Service (ReDoS) causing CPU exhaustion and service disruption.\n\n**Who is impacted:** Any application using the `ca.uhn.hapi.fhir:org.hl7.fhir.dstu2` module that evaluates user-supplied FHIRPath expressions \u2014 including the FHIR Validator HTTP endpoint, FHIR servers applying FHIRPath invariants from user-provided resources or profiles, and any system embedding `FHIRPathEngine` from the DSTU2 module. No authentication is required; an attacker needs only to submit a FHIR resource or FHIRPath expression whose `matches()` argument contains a catastrophically backtracking regular expression.",
  "id": "GHSA-fxj4-p9xp-37v5",
  "modified": "2026-06-17T18:47:23Z",
  "published": "2026-06-17T18:47:23Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/hapifhir/org.hl7.fhir.core/security/advisories/GHSA-fxj4-p9xp-37v5"
    },
    {
      "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: Incomplete fix for CVE-2026-45367: DSTU2 FHIRPathEngine.matches() missing RegexTimeout protection allows ReDoS"
}

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.

Action not permitted

CVE-2026-55470 (GCVE-0-2026-55470)

FKIE_CVE-2026-55470

GHSA-FXJ4-P9XP-37V5

Summary

Details

Incomplete patch

Module-by-module status

PoC

Impact

Tags

Sightings

Nomenclature