CVE-2026-56741

HighCVSS 7.5

Published: 17/07/2026(UTC)Updated: 18/08/2026(UTC)Translated: 24/07/2026(UTC)NVD NIST

Exploitation Probability (EPSS)

Low risk

0.52%

41th percentile - higher than 41% of all known CVEs

Summary

JLine, a Java library for console input, contains a vulnerability in the Telnet server remote-telnet module. The TelnetIO.handleNAWS() function does not limit terminal dimensions received from the client, allowing an unauthenticated attacker to repeatedly set large values (e.g., 65535x65535), causing intensive rendering calculations and CPU exhaustion (DoS).

Risk Assessment

The organization is at risk of a DoS attack on the Telnet server, potentially disrupting console services and affecting system availability.

Recommendation

Update JLine to version 3.30.14, 4.0.16, or 4.2.1, which include an upper bound limit for terminal dimensions.

Other vulnerabilities in JLine

CVE-2026-56740High
JLine is a Java library for console handling. Prior to versions 3.30.14, 4.0.16, and 4.2.1, the Telnet module does not limit the number of environment variables a client can inject. An unauthenticated attacker can send many unique variable pairs, causing JVM heap memory exhaustion and an OutOfMemoryError.

Original NVD description (English source)

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.