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Advisory record · GHSA-2r2c-cx56-8933

JLine3 Telnet server: Unauthenticated Remote DoS via Unbounded Telnet NAWS Terminal Geometry

CVSS 7.5 HighEPSS 0.0060 · 48th percentile

Published by the GitHub Advisory Database at 18 Jun 2026, 13:07 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

PackageEcosystemAffectedFixed in
org.jline:jline-remote-telnetMaven>=4.1.0, <4.2.1 || >=4.0.0, <4.0.16 || <3.30.144.2.1, 4.0.16, 3.30.14
Identifiers
GHSA-2r2c-cx56-8933 · CVE-2026-56741
Weakness (CWE)
CWE-400
Tags
Published
18 Jun 2026
Updated
10 Sept 2026

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

The JLine3 remote-telnet module, affected in org.jline:jline-remote-telnet versions 4.1.0 up to 4.2.1, 4.0.0 up to 4.0.16, and earlier than 3.30.14, does not limit the terminal dimensions a client can report through the Telnet NAWS option. An unauthenticated remote attacker who repeatedly alternates very large window sizes can keep the server busy rendering, exhausting CPU and denying service. Upgrade to 4.2.1, 4.0.16, or 3.30.14, depending on the release line in use.

Written 2 Nov 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

ScoreRatingCVSSVectorSource
7.5 High 3.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H CNA (GitHub_M)
  • CISA KEV Not listed.
  • EPSS 0.0060, the 48th percentile, on 9 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

  1. 31 Oct 2026, 14:16 UTC First seen by agentprime
  2. 31 Oct 2026, 14:16 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.