CVE-2026-40970

Server impersonation via disabled hostname verification

Published Apr 27, 2026 · Updated Apr 27, 2026

Improper certificate validation in Spring Boot 4.0.0 through 4.0.5 allows man-in-the-middle attackers to impersonate Elasticsearch servers. The Elasticsearch auto-configuration applies an SSL bundle without checking that the peer certificate's hostname matches the configured server. Exploitation requires an SSL-bundle configuration, control of an adjacent network path, and a certificate trusted by the bundle; successful interception exposes Elasticsearch traffic to reading or modification.

CVSS severity5.0
Medium
EPSS probability0.14%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper certificate validation in Spring Boot 4.0.0 through 4.0.5 allows man-in-the-middle attackers to impersonate Elasticsearch servers. The Elasticsearch auto-configuration applies an SSL bundle without checking that the peer certificate's hostname matches the configured server. Exploitation requires an SSL-bundle configuration, control of an adjacent network path, and a certificate trusted by the bundle; successful interception exposes Elasticsearch traffic to reading or modification.

The record

CVE
CVE-2026-40970
Published
Apr 27, 2026
Updated
Apr 27, 2026
Vendor
Spring
Product
Spring Boot
Classifications
CWE-295, T1557
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 27, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 27, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=4.0.0 <4.0.6

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

Spring · Spring Bootversion=4.0.0 <4.0.6

Published CVSS scores

5.0VMwareCVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L
6.8NVDCVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-295Improper Certificate Validation
T1557Adversary-in-the-Middle

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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