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Vert.x has a DoS via unbounded server-side SNI SslContext cache growth

Moderate severity GitHub Reviewed Published May 6, 2026 in eclipse-vertx/vert.x • Updated Jun 2, 2026

Package

maven io.vertx:vertx-core (Maven)

Affected versions

>= 4.3.4, <= 4.3.8
>= 4.4.0, <= 4.4.9
>= 4.5.0, <= 4.5.26
>= 5.0.0, <= 5.0.11

Patched versions

4.5.27
5.0.12

Description

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

References

Published by the National Vulnerability Database May 6, 2026
@vietj vietj published to eclipse-vertx/vert.x May 6, 2026
Published to the GitHub Advisory Database May 9, 2026
Reviewed May 9, 2026
Last updated Jun 2, 2026

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity Low
Attack Requirements None
Privileges Required None
User interaction None
Vulnerable System Impact Metrics
Confidentiality None
Integrity None
Availability Low
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability Low

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:L

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(15th percentile)

Weaknesses

Improper Certificate Validation

The product does not validate, or incorrectly validates, a certificate. Learn more on MITRE.

Allocation of Resources Without Limits or Throttling

The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated. Learn more on MITRE.

CVE ID

CVE-2026-6860

GHSA ID

GHSA-3g76-f9xq-8vp6

Source code

Credits

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