Inefficient regular expression complexity in Elasticsearch - CVE-2026-102408
Published: October 7, 2026
Vulnerability identifier: #VU153939
CSH Severity: Low
CVSS v4: 5.3 [CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-102408
CWE-ID: CWE-1333
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote user to cause a denial of service.
The vulnerability exists due to inefficient regular expression complexity in the ES|QL CHUNK function's recursive chunking strategy when processing user-supplied regular expressions as text-splitting separators. A remote user can submit a specially crafted regular expression that triggers catastrophic backtracking and excessive CPU consumption on Elasticsearch worker threads to cause a denial of service.
Exploitation requires read access to a text-family index; the built-in viewer role is sufficient. Query throughput for other tenants on the affected node is degraded, but the cluster does not crash.
Affected software
Elasticsearch
How to mitigate CVE-2026-102408
Install security update from vendor's website.
Elasticsearch - addressed in versions 8.19.22, 9.4.8, 9.5.5