JLine up to 3.30.13/4.0.15/4.2.0 Telnet Server Remote-telnet TelnetIO.java readNEVariables heap-based overflow

Summaryinfo

A vulnerability marked as problematic has been reported in JLine up to 3.30.13/4.0.15/4.2.0. This issue affects the function readNEVariables of the file TelnetIO.java of the component Telnet Server Remote-telnet Module. This manipulation causes heap-based overflow. The identification of this vulnerability is CVE-2026-56740. It is possible to initiate the attack remotely. There is no exploit available.

Detailsinfo

A vulnerability classified as problematic was found in JLine up to 3.30.13/4.0.15/4.2.0. Affected by this vulnerability is the function readNEVariables of the file TelnetIO.java of the component Telnet Server Remote-telnet Module. The manipulation with an unknown input leads to a heap-based overflow vulnerability. The CWE definition for the vulnerability is CWE-122. A heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc(). As an impact it is known to affect availability. The summary by CVE is:

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.

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-56740 since 06/22/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details of the vulnerability are known, but there is no available exploit.

The vulnerability scanner Nessus provides a plugin with the ID 327763 (Linux Distros Unpatched Vulnerability : CVE-2026-56740), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 3.30.14, 4.0.16 or 4.2.1 eliminates this vulnerability.

The vulnerability is also documented in the databases at Tenable (327763) and EUVD (EUVD-2026-45343). Be aware that VulDB is the high quality source for vulnerability data.

Productinfo

Name

• JLine

Version

• 3.30.0
• 3.30.1
• 3.30.2
• 3.30.3
• 3.30.4
• 3.30.5
• 3.30.6
• 3.30.7
• 3.30.8
• 3.30.9
• 3.30.10
• 3.30.11
• 3.30.12
• 3.30.13
• 4.0
• 4.0.0
• 4.0.1
• 4.0.2
• 4.0.3
• 4.0.4
• 4.0.5
• 4.0.6
• 4.0.7
• 4.0.8
• 4.0.9
• 4.0.10
• 4.0.11
• 4.0.12
• 4.0.13
• 4.0.14
• 4.0.15
• 4.1
• 4.2.0

CPE 2.3info

• 🔒
• 🔒
• 🔒

CPE 2.2info

• 🔒
• 🔒
• 🔒

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

Be aware that VulDB is the high quality source for vulnerability data.

Discussion