CVE-2026-77421 JLine: ReDoS in Nano Editor Regex Search Mode
Attackers can cause denial of service in JLine's nano editor by submitting regex patterns that trigger excessive CPU consumption and block threads.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-77421?
CVE-2026-77421 is a medium-severity denial of service vulnerability in jline3, published on 23 Sep 2026. Any signed-in user can exploit it over the 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, 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.
Weakness: CWE-1333
Which versions are affected by CVE-2026-77421?
4 open source packages ship an affected version, including org.jline:jline-builtins.
| Package | Affected | Fixed in |
|---|---|---|
org.jline:jline-builtins Maven | From 3.0.0 | 3.30.15 |
org.jline:jline-builtins Maven | From 3.0.0 | 3.30.15 |
org.jline:jline-builtins Maven | From 4.0.0 | 4.3.1 |
org.jline:jline-builtins Maven | From 4.0.0 | 4.3.1 |
How do I fix CVE-2026-77421?
Upgrade org.jline:jline-builtins 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-2026-77421 being exploited?
There is no known exploitation of CVE-2026-77421 in the wild and no public exploit code.
Sources
Also known as CLEANSTART-2026-AD70544, CLEANSTART-2026-AJ94302, CLEANSTART-2026-EP67643, CLEANSTART-2026-IS00308, CLEANSTART-2026-JE20809, CLEANSTART-2026-YP64784 and 20 more.