Inefficient regular expression complexity in FHIR - CVE-2026-55470
Published: July 14, 2026
Vulnerability identifier: #VU137476
CSH Severity: Medium
CVSS v4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-55470
CWE-ID: CWE-1333
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to cause a denial of service.
The vulnerability exists due to inefficient regular expression complexity in FHIRPathEngine.matches() in the DSTU2 module when evaluating user-supplied FHIRPath expressions or resources containing a crafted matches() regular expression. A remote attacker can submit a crafted regular expression that triggers catastrophic backtracking to cause a denial of service.
The issue affects the DSTU2 implementation because the matches() path invokes raw regular expression matching without timeout protection.
Affected software
FHIR
How to mitigate CVE-2026-55470
Install security update from vendor's website.
FHIR - update to 6.9.10