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JlineApplication

CVE-2026-56740

HIGH · 7.5 CVSS v3.1 Developing Published 2026-07-17
Fix available
A fix is available. Upgrade to 3.30.14 / 4.0.16 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click 5 weeks old

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · low confidence
Developing — this CVE was published recently and its authoritative NVD entry is still being established, so we're holding a technical summary until the source data settles rather than publish something unreliable. Re-checking after 2026-07-31.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
JlineApplication
Affected:< 3.30.14>= 4.0.0, < 4.0.16>= 4.1.0, < 4.2.1

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
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

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 3.30.14 / 4.0.16 / 4.2.1 or later
Fixed in 3.30.144.0.164.2.1
Recommended fix High confidence

3.30.14 (for 3.x users), 4.0.16 (for 4.0.x users), or 4.2.1 (for 4.1.x users)

  1. Identify the current JLine version in use by checking project dependencies (Maven pom.xml, Gradle build.gradle, or JAR manifest)
  2. If using JLine 3.x line: upgrade to version 3.30.14 or later
  3. If using JLine 4.0.x line: upgrade to version 4.0.16 or later
  4. If using JLine 4.1.x line: upgrade to version 4.2.1 or later (4.2.1 is the next stable release after 4.1.x)
  5. Update the dependency management in your build configuration
  6. Rebuild and redeploy the application
  7. For production deployments, test the upgrade in a staging environment first to verify compatibility
Caveat Minor: Verify that any custom environment variable handling or Telnet integration works correctly with the updated library, as internal Telnet handling may have changed

Generated from the published advisory — verify against the referenced sources before acting.

We can perform the upgrade in your staging environment and verify nothing breaks — typical engagement from $1,950. Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-56740 in production — separate from our analysis above.

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What this is

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  • Version or environment caveats, and links to real fixes
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