CVE-2026-77420: JLine: ReDoS via `HISTORY_IGNORE` Configuration Variable

Summary

The JLine3 HISTORYIGNORE variable is converted into a Java regular expression with only partial escaping. As a result, regex metacharacters other than and : are passed through to the regex engine. A crafted value such as (a+)+b can cause catastrophic backtracking each time a command line is added to history, hanging the reader thread at high CPU.

Details

In reader/src/main/java/org/jline/reader/impl/history/DefaultHistory.java, matchPatterns() converts HISTORYIGNORE into a regex:

java for (int i = 0; i < patterns.length(); i++) { char ch = patterns.charAt(i); if (ch == '\\') { ch = patterns.charAt(++i); sb.append(ch); } else if (ch == ':') { sb.append('|'); } else if (ch == '') { sb.append('.').append(''); } else { sb.append(ch); } } return line.matches(sb.toString());

This logic translates wildcard syntax but does not escape regex metacharacters such as (, ), +, ?, {, }, [, and ]. Those characters therefore reach the Java regex engine unchanged.

Affected source location: - reader/src/main/java/org/jline/reader/impl/history/DefaultHistory.java - matchPatterns(String patterns, String line)

PoC

1. Configure HISTORYIGNORE to a malicious pattern, for example:

sh set history-ignore "(a+)+b"

2. At the JLine prompt, enter a long non-matching line:

text aaaaaaaaaaaaaaaaaaaaaaaaaaax

3. Press Enter.

Expected result: - The prompt does not return. - The reader 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-reader are impacted if they allow HISTORYIGNORE to be configured through user configuration or application settings. The issue is lower severity than the interactive editor findings because the attacker must control configuration, but it can still reliably hang a reader session.

Suggested Fix

The safest fix for the current git head is to stop treating arbitrary HISTORYIGNORE content as a regex. Instead, escape all characters by default and translate only the intended JLine wildcard syntax () and separator syntax (:).

Suggested patch:

diff diff --git a/reader/src/main/java/org/jline/reader/impl/history/DefaultHistory.java b/reader/src/main/java/org/jline/reader/impl/history/DefaultHistory.java --- a/reader/src/main/java/org/jline/reader/impl/history/DefaultHistory.java +++ b/reader/src/main/java/org/jline/reader/impl/history/DefaultHistory.java @@ StringBuilder sb = new StringBuilder(); for (int i = 0; i < patterns.length(); i++) { char ch = patterns.charAt(i); if (ch == '\\') { ch = patterns.charAt(++i); - sb.append(ch); + sb.append(Pattern.quote(Character.toString(ch))); } else if (ch == ':') { sb.append('|'); } else if (ch == '') { sb.append('.').append(''); } else { - sb.append(ch); + sb.append(Pattern.quote(Character.toString(ch))); } } return line.matches(sb.toString());

Credits

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