CVE-2026-40992: Mail Auto-Configuration Does Not Enable SSL Hostname Verification

Severity: medium (CVSS 5.0 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-06-11 · updated 2026-09-04
Weakness: CWE-295

Description

Spring Boot's Mail auto-configuration does not enable hostname verification. Applications that set the relevant JavaMail property, such as spring.mail.properties.mail.smtp.ssl.checkserveridentity=true, are not affected. Affected versions: Spring Boot 4.0.0 through 4.0.6; 3.5.0 through 3.5.14; 3.4.0 through 3.4.16.

Affected products

Spring Boot: from 3.4.0 before 3.4.17; from 3.5.0 before 3.5.14.1; from 4.0.0 before 4.0.6.1 — fixed in 3.4.17, 3.5.14.1, 4.0.6.1
Spring Boot: from 4.0.0 before 4.0.6.1; from 3.5.0 before 3.5.14.1; from 3.4.0 before 3.4.17 — fixed in 4.0.6.1, 3.5.14.1, 3.4.17

How to fix

Upgrade to a fixed version: Spring Boot 3.4.17, 3.5.14.1, 4.0.6.1; Spring Boot 4.0.6.1, 3.5.14.1, 3.4.17. Check the vendor advisory for mitigations.

References

https://spring.io/security/cve-2026-40992

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