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Vulnerability · Published Jul 17, 2026 · Assigned by GitHub_M

CVE-2026-56741JLine: Unauthenticated Remote DoS via Unbounded Telnet NAWS Terminal Geometry

High 7.5

In plain English

A high-severity uncontrolled resource consumption in jline3 from jline. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 49% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.5High
Exploit odds (30 days)0.6%top 51.4% of all CVEs
Exploited in the wildNo reportsCISA SSVC: poc
Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Debian:12jlineno fix listedDEBIAN-CVE-2026-56741
Debian:13jlineno fix listedDEBIAN-CVE-2026-56741
Debian:14jlineno fix listedDEBIAN-CVE-2026-56741
Debian:12jline2no fix listedDEBIAN-CVE-2026-56741
Debian:13jline2no fix listedDEBIAN-CVE-2026-56741
Debian:14jline2no fix listedDEBIAN-CVE-2026-56741
Debian:12jline3no fix listedDEBIAN-CVE-2026-56741
Debian:13jline3no fix listedDEBIAN-CVE-2026-56741
Debian:14jline3no fix listedDEBIAN-CVE-2026-56741
Mavenorg.jline:jline-remote-telnet4.2.1GHSA-2r2c-cx56-8933
Mavenorg.jline:jline-remote-telnet4.0.16GHSA-2r2c-cx56-8933
Mavenorg.jline:jline-remote-telnet3.30.14GHSA-2r2c-cx56-8933
Ubuntu:22.04:LTSjlineno fix listedUBUNTU-CVE-2026-56741
Ubuntu:24.04:LTSjlineno fix listedUBUNTU-CVE-2026-56741
Ubuntu:26.04:LTSjlineno fix listedUBUNTU-CVE-2026-56741
Ubuntu:26.10jlineno fix listedUBUNTU-CVE-2026-56741
Ubuntu:22.04:LTSjline2no fix listedUBUNTU-CVE-2026-56741
Ubuntu:24.04:LTSjline2no fix listedUBUNTU-CVE-2026-56741
Ubuntu:26.04:LTSjline2no fix listedUBUNTU-CVE-2026-56741
Ubuntu:26.10jline2no fix listedUBUNTU-CVE-2026-56741
Ubuntu:22.04:LTSjline3no fix listedUBUNTU-CVE-2026-56741
Ubuntu:24.04:LTSjline3no fix listedUBUNTU-CVE-2026-56741
Ubuntu:26.04:LTSjline3no fix listedUBUNTU-CVE-2026-56741
Ubuntu:26.10jline3no fix listedUBUNTU-CVE-2026-56741

Affected products (as reported)

VendorProductVersions
jline jline3 < 3.30.14>= 4.0.0, < 4.0.16>= 4.1.0, < 4.2.1

Weakness: CWE-400 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References