CVE-2026-40992
MEDIUMCVE-2026-40992 is a medium-severity (CVSS 5) CWE-295 vulnerability in org.springframework.boot:spring-boot-starter-mail. O3 Security confirms whether CVE-2026-40992 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Spring Boot's Mail Auto-Configuration Does Not Enable SSL Hostname Verification
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-40992.
Real-World Exposure
org.springframework.boot:spring-boot-starter-mail☕org.springframework.boot:spring-boot-starter-mail☕org.springframework.boot:spring-boot-starter-mailReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.
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 Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | org.springframework.boot:spring-boot-starter-mail | ≥ 4.0.0&&< 4.0.7 | 4.0.7 |
| ☕Maven | org.springframework.boot:spring-boot-starter-mail | ≥ 3.5.0&&< 3.5.15 | 3.5.15 |
| ☕Maven | org.springframework.boot:spring-boot-starter-mail | ≥ 3.4.0 | No fix |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.springframework.boot:spring-boot-starter-mail. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update org.springframework.boot:spring-boot-starter-mail to 4.0.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-40992 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-40992 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-40992. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-40992 in your dependencies?
O3 detects CVE-2026-40992 across Maven dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.