CVE-2026-56741 jline CVE debrief

Who should care

Users of JLine versions prior to 3.30.14, 4.0.16, and 4.2.1 should be aware of this vulnerability and take steps to mitigate it. This includes administrators and developers who use JLine in their applications, as well as security teams and vulnerability management teams.

Technical summary

The JLine3 Telnet server remote-telnet module does not apply an upper bound to terminal dimensions received via the Telnet NAWS option. This allows an unauthenticated remote attacker to repeatedly alternate values and trigger continuous expensive rendering work that causes CPU exhaustion and denial of service. The vulnerability is fixed in versions 3.30.14, 4.0.16, and 4.2.1. Affected users should update to these versions or later to mitigate the vulnerability.

Defensive priority

High

Recommended defensive actions

• Update JLine to version 3.30.14, 4.0.16, or 4.2.1 or later
• Restrict access to the Telnet server
• Monitor for suspicious activity
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record was published on 2026-07-17T22:17:57.317Z and has not been modified since then. The NVD entry is currently 7.5 HIGH. Limited evidence is available, and further investigation is recommended. The vulnerability affects JLine versions prior to 3.30.14, 4.0.16, and 4.2.1.

Official resources