CVE-2026-56741

JLine: Unauthenticated Remote DoS via Unbounded Telnet NAWS Terminal Geometry

Published Jul 17, 2026 CVSS 3.1 · 7.5 High EPSS < 1% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Github GHSA Github GHSA GHSA-2r2c-cx56-8933 JLine3 Telnet server: Unauthenticated Remote DoS via Unbounded Telnet NAWS Terminal Geometry
History
Type Values Removed Values Added
CPEs cpe:2.3:a:jline:jline:*:*:*:*:*:*:*:*
Type Values Removed Values Added
First Time appeared Jline
Jline jline
Vendors & Products Jline
Jline jline
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
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.
Title JLine: Unauthenticated Remote DoS via Unbounded Telnet NAWS Terminal Geometry
Weaknesses CWE-400
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
GitHub_M
Published
Updated
Jul 20, 2026, 3:21 PM
Reserved
Jun 22, 2026, 7:17 PM
Status
Analyzed
Published
Jul 17, 2026, 10:17 PM
Modified
Oct 24, 2026, 8:10 PM