CVE-2026-56741Public exploitNetwork attack vector

Unauthenticated service interruption via unbounded NAWS geometry

Published Jul 17, 2026 · Updated Jul 17, 2026

Resource exhaustion in JLine remote-telnet before 3.30.14, 4.0.16, and 4.2.1 allows remote attackers to interrupt service via Telnet NAWS. TelnetIO.handleNAWS() accepts 16-bit client width and height values without upper bounds, then propagates them through setTerminalGeometry() into repeated redisplay work. Exposure requires an application to embed the module and expose its Telnet server; alternating oversized values can occupy a connection thread and exhaust CPU.

CVSS severity7.5
High
EPSS probability0.60%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Resource exhaustion in JLine remote-telnet before 3.30.14, 4.0.16, and 4.2.1 allows remote attackers to interrupt service via Telnet NAWS. TelnetIO.handleNAWS() accepts 16-bit client width and height values without upper bounds, then propagates them through setTerminalGeometry() into repeated redisplay work. Exposure requires an application to embed the module and expose its Telnet server; alternating oversized values can occupy a connection thread and exhaust CPU.

The record

CVE
CVE-2026-56741
Published
Jul 17, 2026
Updated
Jul 17, 2026
Vendor
JLine
Product
JLine
Classifications
CWE-400, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 17, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 17, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 3.30.14
  2. Affected versionversion=>= 4.0.0, < 4.0.16
  3. Affected versionversion=>= 4.1.0, < 4.2.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

JLine · JLineversion=< 3.30.14; version=>= 4.0.0, < 4.0.16; version=>= 4.1.0, < 4.2.1

Published CVSS scores

7.5GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-400Uncontrolled Resource Consumption
T1499.004Endpoint Denial of Service: Application or System Exploitation

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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