CVE-2026-56740
Description
A flaw was found in the JLine3 Telnet server remote-telnet module. An unauthenticated remote attacker can exploit this vulnerability by injecting an excessive number of environment variables through the Telnet NEW-ENVIRON option. This action causes the server to store numerous variable pairs, leading to the exhaustion of Java Virtual Machine (JVM) heap memory and a Denial of Service (DoS) condition.
Statement
This is a denial of service vulnerability in the JLine3 Telnet server module. An unauthenticated remote attacker can exploit this flaw by injecting excessive environment variables, leading to JVM heap memory exhaustion and a denial of service in applications that expose this vulnerable Telnet server functionality.
Mitigation
To mitigate this issue, restrict network access to applications that expose the JLine3 Telnet server module. If the Telnet server functionality is not required, consider disabling the JLine3 remote-telnet module within the affected application's configuration. Consult application-specific documentation for instructions on disabling or configuring the Telnet server. A restart of the affected application or service may be required for changes to take effect.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.5 | N/A | 7.5 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | None | N/A | None |
| Integrity Impact | None | N/A | None |
| Availability Impact | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Resource Consumption (CPU); DoS: Resource Consumption (Memory); DoS: Resource Consumption (Other)
When allocating resources without limits, an attacker could prevent other systems, applications, or processes from accessing the same type of resource. It can be easy for an attacker to consume many resources by rapidly making many requests or causing larger resources to be used than is needed.
Frequently Asked Questions
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