# CVE-2026-56741: JLine: Unauthenticated Remote DoS via Unbounded Telnet NAWS Terminal Geometry > An unauthenticated remote attacker can cause CPU exhaustion and denial of service in JLine Telnet servers by sending unbounded terminal geometry values. - **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 17 Jul 2026 - **Updated:** 20 Jul 2026 - **Also known as:** AZL-92453, CLEANSTART-2026-JV45560, CLEANSTART-2026-OL13486, CLEANSTART-2026-ZL99658, DEBIAN-CVE-2026-56741, ECHO-dabb-5c9f-5c7d, GHSA-2r2c-cx56-8933, MINI-3wjf-97w7-8qrj, MINI-3xm6-383q-h68q, MINI-429g-8vp2-f79x, MINI-53fh-p5c4-8jcx, MINI-5r88-44x7-8hcv, MINI-63hr-xm4r-4wj2, MINI-6987-m49g-239c, MINI-6gr5-rgxw-39jq, MINI-7fv8-xx2j-w8g9, MINI-7vgh-8vwq-m85j, MINI-85hh-5g28-hpx8, MINI-85rh-wp8w-vf4r, MINI-987g-6g2r-r6p2, MINI-9qm4-79xr-rjrq, MINI-9rc3-vh85-8xx2, MINI-c25g-r633-25mq, MINI-c3gj-5f25-gc7f, MINI-f3xp-fw2m-m535, MINI-f5q3-pcmc-vvmf, MINI-fvgr-56wj-g5q7, MINI-hxr8-88ww-xjj2, MINI-jf27-r57w-626g, MINI-m4h8-9rf3-hx4r, MINI-mr8g-869g-gfch, MINI-mxhp-469c-cmqf, MINI-r8pw-p38v-vqx8, MINI-rch7-q2pj-c4cp, MINI-rp57-7g97-2vrf, MINI-w339-4xm5-p8rx, MINI-xhvw-pw9p-553q, ROOT-APP-MAVEN-CVE-2026-56741, ROOT-APP-MAVEN-GHSA-2r2c-cx56-8933, UBUNTU-CVE-2026-56741 ## What is CVE-2026-56741? CVE-2026-56741 is a high-severity denial of service vulnerability in jline3, published on 17 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. ### Official 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. Weakness: CWE-400 (Uncontrolled Resource Consumption) ## Which versions are affected by CVE-2026-56741? 6 open source packages ship an affected version, including org.jline:jline-remote-telnet. It affects 1 product. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `org.jline:jline-remote-telnet` | Maven | All versions | 3.30.14 | | `org.jline:jline-remote-telnet` | Maven | All versions | 3.30.14 | | `org.jline:jline-remote-telnet` | Maven | From 4.0.0 | 4.0.16 | | `org.jline:jline-remote-telnet` | Maven | From 4.0.0 | 4.0.16 | | `org.jline:jline-remote-telnet` | Maven | From 4.1.0 | 4.2.1 | | `org.jline:jline-remote-telnet` | Maven | From 4.1.0 | 4.2.1 | Products: Jline Jline. ## How do I fix CVE-2026-56741? Upgrade org.jline:jline-remote-telnet to a fixed version for your release line: 3.30.14, 4.0.16 or 4.2.1. ## Is CVE-2026-56741 being exploited? It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-56741 exists. ## Other vulnerabilities in jline3 - [CVE-2026-56740](https://insights.sbomify.com/CVE-2026-56740/): JLine: Unauthenticated Remote Memory Exhaustion via Unbounded Telnet NEW-ENVIRON Variables (high 7.5) - [CVE-2023-50572](https://insights.sbomify.com/CVE-2023-50572/): JLine vulnerable to out of memory error (medium 5.5) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-56741 and fix it if it is affected. What it is: CVE-2026-56741 is a high-severity denial of service vulnerability in jline3, published on 17 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-56741 exists. Affected packages and fixed versions: - org.jline:jline-remote-telnet (Maven): affected all versions; fixed in 3.30.14 - org.jline:jline-remote-telnet (Maven): affected all versions; fixed in 3.30.14 - org.jline:jline-remote-telnet (Maven): affected from 4.0.0; fixed in 4.0.16 - org.jline:jline-remote-telnet (Maven): affected from 4.0.0; fixed in 4.0.16 - org.jline:jline-remote-telnet (Maven): affected from 4.1.0; fixed in 4.2.1 - org.jline:jline-remote-telnet (Maven): affected from 4.1.0; fixed in 4.2.1 Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2026-56741/ (Markdown: https://insights.sbomify.com/CVE-2026-56741/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-56741 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-56741 - OSV: https://osv.dev/vulnerability/CVE-2026-56741 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-56741/ Summaries are generated and may contain mistakes; the official description above is the record.