CVE-2026-77421: JLine: ReDoS in Nano Editor Regex Search Mode

Summary

When regex search mode is enabled in the JLine3 nano editor, the user-supplied search term is compiled directly as a Java regular expression with no timeout or backtracking bound. A crafted pattern such as (a+)+b can hang the editor session thread at high CPU, causing a denial of service for that session.

Details

In builtins/src/main/java/org/jline/builtins/Nano.java, the search implementation uses Pattern.LITERAL only when regex mode is disabled. When regex mode is enabled, the search term is compiled as a raw Java regex:

java Pattern pat = Pattern.compile( searchTerm, (searchCaseSensitive ? 0 : Pattern.CASEINSENSITIVE | Pattern.UNICODECASE) | (searchRegexp ? 0 : Pattern.LITERAL));

This regex is then applied to buffer content. Because Java's regex engine is backtracking-based, nested-quantifier patterns can take exponential time on non-matching input.

Affected source location: - builtins/src/main/java/org/jline/builtins/Nano.java - doSearch(String text)

PoC

1. Create a file containing a long run of a characters and open it in the JLine3 nano editor. 2. Enable regex search mode with the editor's regex toggle. 3. Start a search and enter the pattern (a+)+b.

Expected result: - The editor stops responding. - The session thread consumes high CPU.

Reproduction environment: - JLine3 on x8664 Linux - OpenJDK 25.0.2

Impact

This is a denial-of-service vulnerability caused by catastrophic regex backtracking. Applications embedding org.jline:jline-builtins and exposing the nano editor are impacted. In local use, the user can hang their own session. In remote multi-user deployments, an attacker can occupy a server worker thread indefinitely.

Suggested Fix

The preferred fix for the current git head is to use a linear-time regex engine for regex search mode while preserving literal matching behavior when regex mode is off.

Suggested patch:

diff diff --git a/builtins/pom.xml b/builtins/pom.xml --- a/builtins/pom.xml +++ b/builtins/pom.xml @@ <dependency> + <groupId>com.google.re2j</groupId> + <artifactId>re2j</artifactId> + <version>1.8</version> + </dependency> + <dependency> <groupId>org.jline</groupId> <artifactId>jline-reader</artifactId> </dependency>

diff --git a/builtins/src/main/java/org/jline/builtins/Nano.java b/builtins/src/main/java/org/jline/builtins/Nano.java --- a/builtins/src/main/java/org/jline/builtins/Nano.java +++ b/builtins/src/main/java/org/jline/builtins/Nano.java @@ -import java.util.regex.Pattern; +import com.google.re2j.Pattern;

If a dependency change is not acceptable, a fallback mitigation is to reject dangerous regex constructs or execute regex matching with a strict timeout, but that is weaker than replacing the backtracking engine.

Credits

This issue was identified by Michał Majchrowicz and Marcin Wyczechowski, members of the AFINE Team.