JLine is a Java library for handling console input. From 3.0.0 until 3.30.15 and 4.3.1, the JLine built-in nano editor's regex search mode passes a user-controlled search term from doSearch(String text) in builtins/src/main/java/org/jline/builtins/Nano.java to Java's backtracking regular expression engine without a timeout or backtracking bound. A nested-quantifier expression evaluated against non-matching buffer content can consume excessive CPU and indefinitely block the editor session thread, and remote multi-user deployments can lose a worker thread for each affected session. This issue is fixed in versions 3.30.15 and 4.3.1.
CVE-2026-77421
MEDIUMPre-NVD 6.56.5—Trending — 3 sources updated this week
EchelonGraph scoreMEDIUM confidence
This medium-severity CVE scores 6.5 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.4%, top 65% 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
6.5EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
- Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 6.5Exploit: None knownExposed: 0
No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.
- CVSS v3
- 6.5
- EG Score
- 6.5(medium)
- EG Risk
- 29(Track)EG Risk 29/100SSVC: Track
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 computedSeverity65% × 45%Exploitation0% × 40%Automatability0% × 15%Action: Routine — remediate on your standard cadence. - EPSS PROB
- 0%
- EPSS %ILE
- 35%
- KEV
- Not listed
Published
September 23, 2026
Last Modified
September 23, 2026
Advisory Details (7)
Auto-updated Sep 23, 2026🔬 Proof of concept available. Patch available. Sources: github_commit, github_release, github, github_pr.
github_release Patch Available
JLine 3.30.15
Patch available: jline/jline3 jline-3.30.15
https://github.com/jline/jline3/releases/tag/jline-3.30.15github_release Patch Available
JLine 4.3.1
Patch available: jline/jline3 4.3.1
https://github.com/jline/jline3/releases/tag/4.3.1github_commit Patch Available
commit 341ee69ccc57 (jline/jline3)
Patch available: jline/jline3 jline-3.30.15 (contains commit 341ee69ccc57)
https://github.com/jline/jline3/commit/341ee69ccc57b7733c1b40d6993219b64b3206aegithub_commit Patch Available
commit 1d5fc3099e77 (jline/jline3)
Patch available: jline/jline3 4.3.1 (contains commit 1d5fc3099e77)
https://github.com/jline/jline3/commit/1d5fc3099e77938b971e197211cad2d4fbb17541github_pr Patch Available
[backport jline-3.x] fix: guard regex matching against catastrophic backtracking (ReDoS)
Patch available: jline/jline3 jline-3.30.15 (PR #2018 merged 2026-06-30)
https://github.com/jline/jline3/pull/2018github_pr Patch Available
fix: guard regex matching against catastrophic backtracking (ReDoS)
Patch available: jline/jline3 4.3.1 (PR #2012 merged 2026-06-30)
https://github.com/jline/jline3/pull/2012github Patch Available🟡 PoC Available
ReDoS in Nano Editor Regex Search Mode · Advisory · jline/jline3 · GitHub
https://github.com/jline/jline3/security/advisories/GHSA-ph9c-7hw9-vhhwVendor Advisories for CVE-2026-77421(1)
These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.
Weakness Classification(1)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 7× in last 7d / 7× 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.
- 2026-09-24 22:58 UTCEG score recompute
- 2026-09-24 14:04 UTCEPSS rescore
- 2026-09-23 20:23 UTCEG score recompute
- 2026-09-23 19:53 UTCEG score recompute
- 2026-09-23 19:28 UTCEG score recompute
- 2026-09-23 18:22 UTCEG score recompute
- 2026-09-23 18:21 UTCMITRE cvelistV5first tracked
Related CVEs(same CWE)
Frequently asked(5)
What is CVE-2026-77421?
CVE-2026-77421 is a medium vulnerability published on September 23, 2026. JLine is a Java library for handling console input. From 3.0.0 until 3.30.15 and 4.3.1, the JLine built-in nano editor's regex search mode passes a user-controlled search term from doSearch(String text) in builtins/src/main/java/org/jline/builtins/Nano.java to Java's backtracking regular expression…
When was CVE-2026-77421 disclosed?
CVE-2026-77421 was first published in the National Vulnerability Database on September 23, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-77421 actively exploited?
CVE-2026-77421 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 65.1% of all scored CVEs.
What is the CVSS score of CVE-2026-77421?
CVE-2026-77421 has a CVSS v3 base score of 6.5 (NVD).
How do I remediate CVE-2026-77421?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-77421, 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
Explore the affected products and dependency analysis for CVE-2026-77421
Is Your Infrastructure Affected by CVE-2026-77421?
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