CVE-2026-56740: JLine: Unauthenticated Remote Memory Exhaustion via Unbounded Telnet NEW-ENVIRON Variables
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 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-2026-56740?
CVE-2026-56740 has a severity rating of 7.5, indicating a high level of risk.
What is the main issue described in CVE-2026-56740?
CVE-2026-56740 involves unauthenticated remote memory exhaustion due to unbounded Telnet NEW-ENVIRON variables in the JLine library.
How do I fix CVE-2026-56740?
To mitigate CVE-2026-56740, update to JLine versions 3.30.14, 4.0.16, or 4.2.1 where the issue has been resolved.
What software is affected by CVE-2026-56740?
CVE-2026-56740 affects the JLine library used for handling console input in Java applications.
What type of vulnerability is CVE-2026-56740?
CVE-2026-56740 is a memory exhaustion vulnerability that can be exploited via unbounded environment variables in Telnet.