VulnerabilityPublished 23 Sep 2026

CVE-2026-77421: jline jline3 · ReDoS

Affects jline jline3Source CVE Database V5

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Not known to be exploited · CVSS 6.5 Medium : upgrade to 4.3.1 or 3.30.15 when convenient.

Data as of 6 Nov 2026, 23:24 UTC

CVSS 3.1 base score

6.5Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.4% chance of exploitation in 30 days – higher than 37% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 4.3.1, 3.30.15

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Attack Vector: Network
Attack Complexity: Low
Privileges Required: Low
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 23 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 7 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade jline3 and org.jline/jline3 to 4.3.1 or 3.30.15.

Affected software

Product	Affected	Fixed in
jlinejline3	Affected >=4.0.0 <4.3.1	Fixed in 4.3.1
jlinejline3	Affected >=3.0.0 <3.30.15	Fixed in 3.30.15
Mavenorg.jline/jline3`pkg:maven/org.jline/jline3`Other threats	Affected >=3.0.0 <3.30.15 >=4.0.0 <4.3.1	Fixed in 3.30.15 4.3.1

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A fix is available in JLine3 versions 3.30.15 and 4.3.1. Users should upgrade to these or later versions to remediate the vulnerability. No additional mitigation is indicated by the vendor advisory.

Description

JLine3 versions from 3.0.0 up to but not including 3.30.15, and from 4.0.0 up to but not including 4.3.1, contain an inefficient regular expression complexity vulnerability in the built-in nano editor's regex search mode. This flaw allows a crafted search term to cause excessive CPU consumption and indefinite blocking of the editor session thread due to unbounded backtracking in Java's regex engine. The issue can lead to denial of service by exhausting worker threads in remote multi-user deployments. The vulnerability is fixed in versions 3.30.15 and 4.3.1.

Impact

The vulnerability results in a denial of service condition by causing the nano editor session thread to block indefinitely due to excessive CPU consumption triggered by complex regex patterns. This can lead to loss of worker threads in remote multi-user deployments, potentially impacting availability. There is no impact on confidentiality or integrity.

Summary

The vulnerability (CVE-2026-77421) affects the JLine3 Java library's built-in nano editor. Specifically, the doSearch(String text) method passes user-controlled search terms to Java's backtracking regex engine without any timeout or backtracking limits. When a nested-quantifier regex pattern is evaluated against non-matching content, it can cause excessive CPU usage and indefinitely block the editor session thread. This can degrade service availability, especially in remote multi-user environments where each affected session may consume a worker thread. The issue is resolved in JLine3 versions 3.30.15 and 4.3.1.

CWE-1333Inefficient Regular Expression Complexity (opens in a new tab)
Base weaknessLikelihood of exploit: High
The product uses a regular expression with a worst-case computational complexity that is inefficient and possibly exponential.
Architecture and Design
Use regular expressions that do not support backtracking, e.g. by removing nested quantifiers.
System Configuration
Set backtracking limits in the configuration of the regular expression implementation, such as PHP's pcre.backtrack_limit. Also consider limits on execution time for the process.
Implementation
Do not use regular expressions with untrusted input. If regular expressions must be used, avoid using backtracking in the expression.
OWASP Cheat Sheets
File Upload (opens in a new tab)
OWASP ASVS 4.0.3
V12.1.1 (opens in a new tab)
Attack patterns
Regular Expression Exponential Blowup (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 17 Oct 2026, 23:41 UTC

WeaknessesCWE-1333

Technical details

References

Community reviews

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