CVE-2026-6860

Potential unbounded server-side SNI SslContext cache growth in Vert.x TLS handling, with = resource-exhaustion / DoS impact. On affected versions, matching server-side SNI names are cached via computeIfAbsent(serverName, ...) in a serverName-keyed SslContext cache.

The implementation differs slightly by branch, but the same sink appears to be present in released versions 4.3.4 through 5.0.11:

• 4.3.x: SSLHelper
• 4.4.x / 4.5.x: SslChannelProvider
• 5.0.x and current master: SslContextProvider

When server-side SNI is enabled and wildcard or otherwise broad hostname mappings are used, an unauthenticated client can send many distinct matching SNI names and cause the server to retain increasing numbers of SslContext entries over time, leading to increasing memory consumption and possible DoS conditions.

Steps to reproduce

1. Configure a Vert.x server with setSsl(true) and setSni(true).
2. Use a keystore or mapping where many distinct SNI names match a wildcard or similarly broad rule.
3. Send repeated connections with distinct matching SNI values.
4. Observe that the SNI cache size grows with the number of unique matching names.

What are the affected versions?

Affected released versions confirmed on origin:

• 4.3.4 through 4.3.8
• 4.4.0 through 4.4.9
• 4.5.0 through 4.5.26
• 5.0.0 through 5.0.11

Not affected by the same sink:

• 4.0.x through 4.2.x
• 4.3.0 through 4.3.3

The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap. Typical impact: resource exhaustion leading to denial of service.

CVE-2026-6860 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.5.27, 5.0.12); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-6860? CVE-2026-6860 is a medium-severity allocation of resources without limits or throttling vulnerability in io.vertx:vertx-core (maven), affecting versions >= 4.3.4, <= 4.3.8. It is fixed in 4.5.27, 5.0.12. The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap.
2. How severe is CVE-2026-6860? CVE-2026-6860 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of io.vertx:vertx-core are affected by CVE-2026-6860? io.vertx:vertx-core (maven) versions >= 4.3.4, <= 4.3.8 is affected.
4. Is there a fix for CVE-2026-6860? Yes. CVE-2026-6860 is fixed in 4.5.27, 5.0.12. Upgrade to this version or later.
5. Is CVE-2026-6860 exploitable, and should I be worried? Whether CVE-2026-6860 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-6860 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-6860?
   • Upgrade io.vertx:vertx-core to 4.5.27 or later
   • Upgrade io.vertx:vertx-core to 5.0.12 or later