# Elasticsearch 8.19.20, 9.4.5, 9.5.1 Security Update (ESA-2026-141)

**URL:** <https://discuss.elastic.co/t/elasticsearch-8-19-20-9-4-5-9-5-1-security-update-esa-2026-141/390092>\
**Category:** Security Announcements\
**Created:** [September 1, 2026, 6:46pm UTC](https://discuss.elastic.co/t/elasticsearch-8-19-20-9-4-5-9-5-1-security-update-esa-2026-141/390092 "2026-09-01T18:46:43Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![ismisepaul](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/ismisepaul/32/102235_2.png) [@ismisepaul](https://discuss.elastic.co/u/ismisepaul)\
**Post date:** [September 1, 2026, 6:46pm UTC](https://discuss.elastic.co/t/elasticsearch-8-19-20-9-4-5-9-5-1-security-update-esa-2026-141/390092/1 "2026-09-01T18:46:43Z")

</div>

**Inconsistent Interpretation of HTTP Requests ('HTTP Request Smuggling') in Elasticsearch Leading to Information Disclosure**

Inconsistent Interpretation of HTTP Requests ('HTTP Request Smuggling') (CWE-444) in Elasticsearch can lead to information disclosure via HTTP Request Smuggling (CAPEC-33). Under specific proxy deployment configurations, a network attacker could obtain confidential responses intended for other authenticated users.

**Affected Versions:**

> - 8.x: All versions from 8.18.0 up to and including 8.19.19
> - 9.x:

- All versions from 9.0.0 up to and including 9.4.4
- Version 9.5.0

**Affected Configurations:**  
The underlying defect is present in all Elasticsearch deployments running an affected version that expose an HTTP/1.1 listener. Successful cross-user response disclosure additionally requires an intermediate proxy or load balancer that shares and reuses persistent backend connections across independent client sessions.

**Solutions and Mitigations:**

The issue is resolved in Elasticsearch versions 8.19.20, 9.4.5, and 9.5.1.

**For Users that Cannot Upgrade:**

**Self-Managed**  
Configure any intermediate proxy or load balancer not to reuse backend connections across independent client sessions. This prevents the cross-user response disclosure, but does not remediate the underlying HTTP framing defect in Elasticsearch itself.

**Cloud**  
There are no workarounds for Elastic Cloud Hosted deployments. Users should upgrade to a fixed version.

**Indicators of Compromise (IOC)**

No specific indicators of compromise have been identified for this vulnerability.

**Elastic Cloud Serverless**

Due to our continuous deployment and patching model, the vulnerability described in this security advisory was remediated in our Elastic Cloud Serverless offering before the public disclosure.

**Severity:** CVSSv3.1: Medium ( 5.9 ) - CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N  
**CVE ID:** CVE-2026-78605  
**Problem Type:** CWE-444 - Inconsistent Interpretation of HTTP Requests ('HTTP Request Smuggling')  
**Impact:** CAPEC-33 - HTTP Request Smuggling