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CVE-2026-56740

Jline denial of service

7.5 HIGHPublic exploitEPSS 0.88%
  1. Published17 Jul 2026

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 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.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityNone
IntegrityNone
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

Jline≥ 4.0.0 < 4.0.16 · ≥ 4.1.0 < 4.2.1 · < 3.30.14

Remediation

Fixed in
Jline≥ 4.0.16

References

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Frequently asked

Is CVE-2026-56740 being actively exploited?

CVE-2026-56740 is not in the CISA KEV catalog. A public exploit reference exists, so treat it as exploitable. Its EPSS exploit probability is 0.88%.

How severe is CVE-2026-56740?

CVE-2026-56740 has a CVSS 3.1 base score of 7.5, rated high. EPSS estimates a 0.88% probability of exploitation.

Which products are affected by CVE-2026-56740?

Affected products include Jline.

How do I fix CVE-2026-56740?

Upgrade affected software to a fixed version, for example Jline 4.0.16 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-56740 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.