What is CVE-2026-56740?

CVE-2026-56740 is a high-severity vulnerability in Jline, classified under Uncontrolled Resource Consumption. CVSS score: 7.5/10. Published 2026-07-17.

How severe is CVE-2026-56740?

High severity. CVSS v3 base score is 7.5 out of 10.

Resource exhaustion in Jline

CVE-2026-56740

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.

Vulnerability class: DoS (Denial of Service)

Published 2026-07-17 · last modified 2026-08-18.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.009 (58.9th percentile), scored 2026-10-24.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 59th percentile — 58.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.009 · newest: 0.009 · change: 0.000

Affected products

Jline
Jline Jline3 — versions < 3.30.14, >= 4.0.0, < 4.0.16, >= 4.1.0, < 4.2.1

Weakness classification (CWE)

CWE-400 — Uncontrolled Resource Consumption

References

github.com/jline/jline3/security/advisories/GHSA-47qp-hqvx-6r3f (Exploit, Vendor Advisory)
github.com/jline/jline3/pull/2000 (Issue Tracking)
github.com/jline/jline3/pull/2001 (Issue Tracking)
github.com/jline/jline3/commit/0389f0ee6d0375901b602671ad5dafd4d1d4ee09 (Patch)
github.com/jline/jline3/commit/4ee3a73849ffb9a85ec748e4e8cd8f6d81f84f40 (Patch)
github.com/jline/jline3/commit/934f09e6128cee33c2b13d42b6e859c1ee2d194b (Patch)
github.com/jline/jline3/releases/tag/4.0.16 (Release Notes)
github.com/jline/jline3/releases/tag/4.2.1 (Release Notes)
github.com/jline/jline3/releases/tag/jline-3.30.14 (Release Notes)

Frequently asked questions

What is CVE-2026-56740?: CVE-2026-56740 is a high-severity vulnerability in Jline, classified under Uncontrolled Resource Consumption. CVSS score: 7.5/10. Published 2026-07-17.
How severe is CVE-2026-56740?: High severity. CVSS v3 base score is 7.5 out of 10.