CVE-2026-56740: Jline

High severity, CVSS 7.5. EPSS: 0.9% chance of exploitation in the next 30 days.

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 limit the number of environment variables a client may inject via the Telnet NEW-ENVIRON option, and TelnetIO.readNEVariables() in TelnetIO.java:1127-1180 stores each variable pair in a HashMap held by ConnectionData, allowing an unauthenticated attacker to flood unique variable pairs before the terminating IAC SE byte and exhaust JVM heap memory with an OutOfMemoryError. This issue is fixed in versions 3.30.14, 4.0.16, and 4.2.1.

Affected products

• Jline Jline: before 3.30.14 (fixed in 3.30.14); from 4.0.0, before 4.0.16 (fixed in 4.0.16); from 4.1.0, before 4.2.1 (fixed in 4.2.1)

Published 2026-07-17. Last modified 2026-08-18.