CVE-2026-56741 JLine: Unauthenticated Remote DoS via Unbounded Telnet NAWS Terminal Geometry
An unauthenticated remote attacker can cause CPU exhaustion and denial of service in JLine Telnet servers by sending unbounded terminal geometry values.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-56741?
CVE-2026-56741 is a high-severity denial of service vulnerability in jline3, published on 17 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-400
Which versions are affected by CVE-2026-56741?
6 open source packages ship an affected version, including org.jline:jline-remote-telnet. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
org.jline:jline-remote-telnet Maven | All versions | 3.30.14 |
org.jline:jline-remote-telnet Maven | All versions | 3.30.14 |
org.jline:jline-remote-telnet Maven | From 4.0.0 | 4.0.16 |
org.jline:jline-remote-telnet Maven | From 4.0.0 | 4.0.16 |
org.jline:jline-remote-telnet Maven | From 4.1.0 | 4.2.1 |
org.jline:jline-remote-telnet Maven | From 4.1.0 | 4.2.1 |
Products include Jline Jline.
How do I fix CVE-2026-56741?
Upgrade org.jline:jline-remote-telnet to a fixed version for your release line: 3.30.14, 4.0.16 or 4.2.1.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-56741 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-56741 exists.
Other vulnerabilities in jline3
Sources
Also known as AZL-92453, CLEANSTART-2026-JV45560, CLEANSTART-2026-OL13486, CLEANSTART-2026-ZL99658, DEBIAN-CVE-2026-56741, ECHO-dabb-5c9f-5c7d and 34 more.