CVE-2026-34361: FHIR Validator HTTP service has SSRF via /loadIG Chains with startsWith() Credential Leak for Authentication Token Theft

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. 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 0.4%, percentile 35: FIRST’s model estimates a 0.4% chance of exploitation activity in the next 30 days, higher than 35% 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.validation (Maven) < 6.9.4, fixed in 6.9.4. 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 version 6.9.4, the FHIR Validator HTTP service exposes an unauthenticated "/loadIG" endpoint that makes outbound HTTP requests to attacker-controlled URLs. Combined with a startsWith() URL prefix matching flaw in the credential provider (ManagedWebAccessUtils.getServer()), an attacker can steal authentication tokens (Bearer, Basic, API keys) configured for legitimate FHIR servers by registering a domain that prefix-matches a configured server URL. This issue has been patched in version 6.9.4.

From the GitHub advisory

Summary

The FHIR Validator HTTP service exposes an unauthenticated /loadIG endpoint that makes outbound HTTP requests to attacker-controlled URLs. Combined with a startsWith() URL prefix matching flaw in the credential provider (ManagedWebAccessUtils.getServer()), an attacker can steal authentication tokens (Bearer, Basic, API keys) configured for legitimate FHIR servers by registering a domain that prefix-matches a configured server URL.

Details

Step 1 — SSRF Entry Point (LoadIGHTTPHandler.java:35-43):

The /loadIG endpoint accepts unauthenticated POST requests with a JSON body containing an ig field. The value is passed directly to IgLoader.loadIg() with no URL validation or allowlisting. When the value is an HTTP(S) URL, IgLoader.fetchFromUrlSpecific() makes an outbound GET request via ManagedWebAccess.get():

Weakness type: CWE-552, CWE-522.

Product: ca.uhn.hapi.fhir:org.hl7.fhir.validation (Maven) · Assigned by: GitHub_M · Published: 2026-03-31

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: changed (can affect other components)

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): 0.42% probability of exploitation activity in the next 30 days; percentile 35.

Timeline

• 2026-03-30 — GitHub-reviewed advisory GHSA-vr79-8m62-wh98 published (critical)
• 2026-03-31 — CVE record last updated
• 2026-03-31 — CVE record published by GitHub_M

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-vr79-8m62-wh98 github.com
2. CVE.org record CVE-2026-34361 cve.org
3. NVD entry CVE-2026-34361 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com

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