JLine prior 3.30.14/4.0.16/4.2.1 Telnet server remote-telnet module TelnetIO.java handleNAWS width/height resource consumption

Summaryinfo

A vulnerability, which was classified as problematic, has been found in JLine. Impacted is the function handleNAWS of the file TelnetIO.java of the component Telnet server remote-telnet module. Performing a manipulation of the argument width/height results in resource consumption. This vulnerability is cataloged as CVE-2026-56741. It is possible to initiate the attack remotely. There is no exploit available.

Detailsinfo

A vulnerability classified as problematic has been found in JLine. This affects the function handleNAWS of the file TelnetIO.java of the component Telnet server remote-telnet module. The manipulation of the argument width/height with an unknown input leads to a resource consumption vulnerability. CWE is classifying the issue as CWE-400. The product does not properly control the allocation and maintenance of a limited resource, thereby enabling an actor to influence the amount of resources consumed, eventually leading to the exhaustion of available resources. This is going to have an impact on availability. The summary by CVE is:

JLine is a Java library for handling console input. Prior to 3.30.14, 4.0.16, and 4.2.1, the JLine3 Telnet server remote-telnet module does not apply an upper bound to terminal dimensions received via the Telnet NAWS option, and TelnetIO.handleNAWS() in TelnetIO.java:856-879 reads client-supplied width and height as 16-bit unsigned integers and passes values such as 65535x65535 to setTerminalGeometry(), allowing an unauthenticated remote attacker to repeatedly alternate values and trigger continuous expensive rendering work that causes CPU exhaustion and denial of service. This issue is fixed in versions 3.30.14, 4.0.16, and 4.2.1.

The advisory is shared at github.com. This vulnerability is uniquely identified as CVE-2026-56741 since 06/22/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1499 for this issue.

Upgrading to version 3.30.14, 4.0.16 or 4.2.1 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-45342). If you want to get the best quality for vulnerability data then you always have to consider VulDB.

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• JLine

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If you want to get the best quality for vulnerability data then you always have to consider VulDB.

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