CVE-2026-77420 JLine: ReDoS via `HISTORY_IGNORE` Configuration Variable
An attacker controlling configuration can trigger a ReDoS attack in JLine, causing excessive CPU usage and blocking the reader thread.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-77420?
CVE-2026-77420 is a medium-severity denial of service vulnerability in jline3, published on 23 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official 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.
Weakness: CWE-1333
Which versions are affected by CVE-2026-77420?
4 open source packages ship an affected version, including org.jline:jline-reader.
| Package | Affected | Fixed in |
|---|---|---|
org.jline:jline-reader Maven | From 3.0.0 | 3.30.15 |
org.jline:jline-reader Maven | From 3.0.0 | 3.30.15 |
org.jline:jline-reader Maven | From 4.0.0 | 4.3.1 |
org.jline:jline-reader Maven | From 4.0.0 | 4.3.1 |
How do I fix CVE-2026-77420?
Upgrade org.jline:jline-reader to a fixed version for your release line: 3.30.15 or 4.3.1.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-77420 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-77420 exists.
Sources
Also known as CLEANSTART-2026-AA89451, CLEANSTART-2026-AQ28324, CLEANSTART-2026-HM88327, CLEANSTART-2026-IR34711, CLEANSTART-2026-KE95640, CLEANSTART-2026-MF43595 and 54 more.