JLine: Unauthenticated Remote DoS via Unbounded Telnet NAWS Terminal Geometry

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Summary

CVECVE-2026-56741
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-07-17 22:17:57 UTC
Updated2026-07-20 16:17:05 UTC
DescriptionJLine 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.

Risk And Classification

Primary CVSS: v3.1 7.5 HIGH from [email protected]

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS: 0.005210000 probability, percentile 0.408610000 (date 2026-07-20)

Problem Types: CWE-400 | CWE-400 CWE-400: Uncontrolled Resource Consumption

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
3.1CNADECLARED7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Jline Jline3 affected < 3.30.14 Not specified
CNA Jline Jline3 affected >= 4.0.0, < 4.0.16 Not specified
CNA Jline Jline3 affected >= 4.1.0, < 4.2.1 Not specified

References

ReferenceSourceLinkTags
github.com/jline/jline3/security/advisories/GHSA-2r2c-cx56-8933 134c704f-9b21-4f2e-91b3-4a467353bcc0 github.com
github.com/jline/jline3/pull/2000 [email protected] github.com
github.com/jline/jline3/commit/86b7ba7801988aadb1a67555629522a71d603bd3 [email protected] github.com
github.com/jline/jline3/commit/733eb353dca7b0ea0252e724445b6defa29c393e [email protected] github.com
github.com/jline/jline3/releases/tag/4.0.16 [email protected] github.com
github.com/jline/jline3/commit/3ea9cad8699714dc072fade29d36be0d1e23d708 [email protected] github.com
github.com/jline/jline3/releases/tag/4.2.1 [email protected] github.com
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