CVE-2026-55471: HAPI FHIR: XXE in XsltUtilities.saxonTransform via unhardened Saxon TransformerFactory

Should you act?

Normal patch cycle

No exploitation signal; fix it in your next routine update if you are affected. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 0.6%, percentile 46: FIRST’s model estimates a 0.6% chance of exploitation activity in the next 30 days, higher than 46% of all scored CVEs (low). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes ca.uhn.hapi.fhir:org.hl7.fhir.utilities (Maven) <= 6.9.9, fixed in 6.9.10. Check your lockfile, including transitive dependencies.

What it is

HAPI FHIR is a complete implementation of the HL7 FHIR standard for healthcare interoperability in Java. Prior to 6.9.10, org.hl7.fhir.utilities.XsltUtilities saxonTransform(...) overloads instantiated a bare net.sf.saxon.TransformerFactoryImpl() without ACCESSEXTERNALDTD or ACCESSEXTERNALSTYLESHEET restrictions, allowing an attacker who controls or can tamper with transformed XML to trigger XML External Entity injection for local file disclosure and blind XXE or SSRF to arbitrary URLs reachable from the host. This issue is fixed in version 6.9.10.

From the GitHub advisory

Summary

org.hl7.fhir.utilities.XsltUtilities exposes two parallel families of XSLT transform helpers. The transform(...) overloads obtain their TransformerFactory from the project's hardened helper XMLUtil.newXXEProtectedTransformerFactory() (which sets ACCESSEXTERNALDTD="" and ACCESSEXTERNALSTYLESHEET=""). The sibling saxonTransform(...) overloads instead instantiate a bare new net.sf.saxon.TransformerFactoryImpl() with no external-access restriction. A document transformed through any saxonTransform(...) overload is parsed with external general entities and external DTD/parameter entities enabled, so an attacker who controls (or can MITM) the transformed XML obtains XML External Entity injection: local file disclosure and blind XXE / SSRF to arbitrary URLs reachable from the host.

XMLUtil documents that its protected factory "should be the only place where TransformerFactory is instantiated in this project". The saxonTransform overloads violate that contract while their same-file transform siblings honour it.

Affected versions

org.hl7.fhir.utilities (Maven ca.uhn.hapi.fhir:org.hl7.fhir.utilities)

Weakness type: CWE-611.

Product: ca.uhn.hapi.fhir:org.hl7.fhir.utilities (Maven) · Assigned by: GitHub_M · Published: 2026-07-08

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Attack requirements: none
• Privileges required: none (no login)
• User interaction: none

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation poc, automatable yes, technical impact partial.
• FIRST EPSS (model of 2026-10-21): 0.57% probability of exploitation activity in the next 30 days; percentile 46.

Timeline

• 2026-06-17 — GitHub-reviewed advisory GHSA-2f55-g35j-5jmf published (critical)
• 2026-07-08 — CVE record published by GitHub_M
• 2026-07-09 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-2f55-g35j-5jmf github.com
2. CVE.org record CVE-2026-55471 cve.org
3. NVD entry CVE-2026-55471 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com

Critical Maven advisories · Today’s Security Digest