CVE-2026-77420 (CVSS 5.5)

Description

JLine is a Java library for handling console input. From 3.0.0 until 3.30.15 and 4.3.1, DefaultHistory.matchPatterns(String patterns, String line) in reader/src/main/java/org/jline/reader/impl/history/DefaultHistory.java converts the HISTORY_IGNORE configuration value into a Java regular expression while escaping only part of its syntax, allowing other regex metacharacters to reach the backtracking engine. An attacker who can control application or user configuration can supply a nested-quantifier expression that is reevaluated whenever a command is added to history, consuming excessive CPU and indefinitely blocking the reader thread. This issue is fixed in versions 3.30.15 and 4.3.1.

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CVSS v3.1 Score

5.5

MEDIUM

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

EPSS — Exploit Prediction

0.0012

Probability of exploitation

0.02%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-1333 CWE-1333

References

Other References

https://github.com/jline/jline3/commit/1d5fc3099e77938b971e197211cad2d4fbb17541 https://github.com/jline/jline3/commit/341ee69ccc57b7733c1b40d6993219b64b3206ae https://github.com/jline/jline3/pull/2012 https://github.com/jline/jline3/pull/2018 https://github.com/jline/jline3/releases/tag/4.3.1 https://github.com/jline/jline3/releases/tag/jline-3.30.15 https://github.com/jline/jline3/security/advisories/GHSA-5q95-hrpc-m3w3 https://github.com/jline/jline3/security/advisories/GHSA-5q95-hrpc-m3w3

Frequently Asked Questions

What is CVE-2026-77420? +

JLine is a Java library for handling console input. From 3.0.0 until 3.30.15 and 4.3.1, DefaultHistory.matchPatterns(String patterns, String line) in reader/src/main/java/org/jline/reader/impl/history/DefaultHistory.java converts the HISTORY_IGNORE configuration value into a Java regular expression while escaping only part of its syntax, allowing other regex metacharacters to reach the backtracking engine. An attacker who can control application or user configuration can supply a nested-quantifier expression that is reevaluated whenever a command is added to history, consuming excessive CPU and indefinitely blocking the reader thread. This issue is fixed in versions 3.30.15 and 4.3.1. It has a CVSS v3.1 base score of 5.5 (MEDIUM).

How severe is CVE-2026-77420? +

CVE-2026-77420 has a CVSS v3.1 score of 5.5 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0012, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-77420? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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