CVE-2026-56741: JLine: Unauthenticated Remote DoS via Unbounded Telnet NAWS Terminal Geometry
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.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
JLine3 telnet server remote-telnet moduleto a version that resolves this vulnerability.Fixed in 3.30.14 - Upgrade
Upgrade
JLine3 telnet server remote-telnet moduleto a version that resolves this vulnerability.Fixed in 4.0.16 - Upgrade
Upgrade
JLine3 telnet server remote-telnet moduleto a version that resolves this vulnerability.Fixed in 4.2.1
Event History
Frequently Asked Questions
What is the severity of CVE-2026-56741?
CVE-2026-56741 has a high severity rating of 7.5.
How do I fix CVE-2026-56741?
To fix CVE-2026-56741, update JLine to version 3.30.14, 4.0.16, or 4.2.1 or later.
What type of vulnerability is CVE-2026-56741?
CVE-2026-56741 is an unauthenticated remote denial-of-service (DoS) vulnerability.
What are the potential impacts of CVE-2026-56741?
The potential impact of CVE-2026-56741 includes service disruption due to unbounded terminal dimensions.
Which versions of JLine are affected by CVE-2026-56741?
Versions of JLine prior to 3.30.14, 4.0.16, and 4.2.1 are affected by CVE-2026-56741.