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.
CVE-2026-56740
HIGHPre-NVD 7.57.5—Trending — 3 sources updated this weekElevated
EchelonGraph scoreMEDIUM confidence
This high-severity CVE scores 7.5 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.5%, top 60% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).
Triggered by: NVD CVSS baseline
Sources: epss, secondary
7.5
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
- High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 1%CVSS: 7.5Exploit: NoneExposed: 0
No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.
- CVSS v3
- 7.5
- EG Score
- 7.5(medium)
- EG Risk
- 65(Attend)EG Risk 65/100SSVC: Attend
EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).
How it’s computedSeverity75% × 45%Exploitation40% × 40%Automatability100% × 15%Action: Remediate soon — notable exploitation risk. - EPSS
- 40.5%
- KEV
- Not listed
Published
July 17, 2026
Last Modified
July 23, 2026
Advisory Details (9)
Auto-updated Jul 17, 2026🔬 Proof of concept available. Patch available. Sources: github, github_pr, github_commit, github_release.
github_release Patch Available
JLine 3.30.14
Patch available: jline/jline3 jline-3.30.14
https://github.com/jline/jline3/releases/tag/jline-3.30.14github_release Patch Available
JLine 4.2.1
Patch available: jline/jline3 4.2.1
https://github.com/jline/jline3/releases/tag/4.2.1github_release Patch Available
JLine 4.0.16
Patch available: jline/jline3 4.0.16
https://github.com/jline/jline3/releases/tag/4.0.16github_commit Patch Available
commit 934f09e6128c (jline/jline3)
Patch available: jline/jline3 4.2.1 (contains commit 934f09e6128c)
https://github.com/jline/jline3/commit/934f09e6128cee33c2b13d42b6e859c1ee2d194bgithub_commit Patch Available
commit 4ee3a73849ff (jline/jline3)
Patch available: jline/jline3 jline-3.30.14 (contains commit 4ee3a73849ff)
https://github.com/jline/jline3/commit/4ee3a73849ffb9a85ec748e4e8cd8f6d81f84f40github_commit Patch Available
commit 0389f0ee6d03 (jline/jline3)
Patch available: jline/jline3 4.0.16 (contains commit 0389f0ee6d03)
https://github.com/jline/jline3/commit/0389f0ee6d0375901b602671ad5dafd4d1d4ee09github_pr Patch Available
fix: backport telnet DoS mitigations (GHSA-47qp, GHSA-2r2c) to 4.0.x
Patch available: jline/jline3 4.0.16 (PR #2001 merged 2026-06-26)
https://github.com/jline/jline3/pull/2001github_pr Patch Available
fix: backport telnet DoS mitigations (GHSA-47qp, GHSA-2r2c) to 3.x
Patch available: jline/jline3 jline-3.30.14 (PR #2000 merged 2026-06-26)
https://github.com/jline/jline3/pull/2000github Patch Available🟡 PoC Available
Unauthenticated Remote Memory Exhaustion via Unbounded Telnet NEW-ENVIRON Variables · Advisory · jline/jline3 · GitHub
https://github.com/jline/jline3/security/advisories/GHSA-47qp-hqvx-6r3fVendor Advisories for CVE-2026-56740(1)
These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.
Affected Packages
(1 across 1 ecosystem)
Maven(1)
| Package | Vulnerable range | Fixed in | Dependents |
|---|---|---|---|
| org.jline:jline-remote-telnet | 3.10.0 ... 4.2.0 (85 versions) | 4.2.1 | — |
Weakness Classification(1)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 12× in last 7d / 12× in last 30d)
Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.
- 2026-07-23 14:18 UTCEPSS rescore
- 2026-07-23 03:20 UTCEG score recompute
- 2026-07-22 14:08 UTCEPSS rescore
- 2026-07-21 15:25 UTCEPSS rescore
- 2026-07-20 17:57 UTCEG score recompute
- 2026-07-20 17:08 UTCEPSS rescore
- 2026-07-19 14:31 UTCEPSS rescore
- 2026-07-19 14:31 UTCEPSS rescore
- 2026-07-19 02:29 UTCEPSS rescore
- 2026-07-18 00:02 UTCEG score recompute
- 2026-07-17 21:40 UTCEG score recompute
- 2026-07-17 21:39 UTCMITRE cvelistV5first tracked
Frequently asked(5)
What is CVE-2026-56740?
CVE-2026-56740 is a high vulnerability published on July 17, 2026. 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…
When was CVE-2026-56740 disclosed?
CVE-2026-56740 was first published in the National Vulnerability Database on July 17, 2026, with the most recent update on July 23, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-56740 actively exploited?
CVE-2026-56740 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 40.5% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-56740?
CVE-2026-56740 has a CVSS v3 base score of 7.5 (NVD).
How do I remediate CVE-2026-56740?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-56740, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.
Dependency Blast Radius
See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-56740
Is Your Infrastructure Affected by CVE-2026-56740?
EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.