GHSA-PH9C-7HW9-VHHW
Vulnerability from github – Published: 2026-09-23 18:12 – Updated: 2026-09-23 18:12Summary
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:
Pattern pat = Pattern.compile(
searchTerm,
(searchCaseSensitive ? 0 : Pattern.CASE_INSENSITIVE | Pattern.UNICODE_CASE)
| (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
- Create a file containing a long run of
acharacters and open it in the JLine3nanoeditor. - Enable regex search mode with the editor's regex toggle.
- 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 x86_64 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 --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.
{
"affected": [
{
"package": {
"ecosystem": "Maven",
"name": "org.jline:jline-builtins"
},
"ranges": [
{
"events": [
{
"introduced": "4.0.0"
},
{
"fixed": "4.3.1"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "Maven",
"name": "org.jline:jline-builtins"
},
"ranges": [
{
"events": [
{
"introduced": "3.0.0"
},
{
"fixed": "3.30.15"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-77421"
],
"database_specific": {
"cwe_ids": [
"CWE-1333"
],
"github_reviewed": true,
"github_reviewed_at": "2026-09-23T18:12:38Z",
"nvd_published_at": null,
"severity": "MODERATE"
},
"details": "### Summary\n\nWhen regex search mode is enabled in the JLine3 `nano` editor, the user-supplied\nsearch term is compiled directly as a Java regular expression with no timeout or\nbacktracking bound. A crafted pattern such as `(a+)+b` can hang the editor session\nthread at high CPU, causing a denial of service for that session.\n\n### Details\n\nIn `builtins/src/main/java/org/jline/builtins/Nano.java`, the search implementation\nuses `Pattern.LITERAL` only when regex mode is disabled. When regex mode is enabled,\nthe search term is compiled as a raw Java regex:\n\n```java\nPattern pat = Pattern.compile(\n searchTerm,\n (searchCaseSensitive ? 0 : Pattern.CASE_INSENSITIVE | Pattern.UNICODE_CASE)\n | (searchRegexp ? 0 : Pattern.LITERAL));\n```\n\nThis regex is then applied to buffer content. Because Java\u0027s regex engine is\nbacktracking-based, nested-quantifier patterns can take exponential time on\nnon-matching input.\n\nAffected source location:\n- `builtins/src/main/java/org/jline/builtins/Nano.java`\n- `doSearch(String text)`\n\n### PoC\n\n1. Create a file containing a long run of `a` characters and open it in the JLine3\n `nano` editor.\n2. Enable regex search mode with the editor\u0027s regex toggle.\n3. Start a search and enter the pattern `(a+)+b`.\n\nExpected result:\n- The editor stops responding.\n- The session thread consumes high CPU.\n\nReproduction environment:\n- JLine3 on x86_64 Linux\n- OpenJDK 25.0.2\n\n### Impact\n\nThis is a denial-of-service vulnerability caused by catastrophic regex backtracking.\nApplications embedding `org.jline:jline-builtins` and exposing the `nano` editor are\nimpacted. In local use, the user can hang their own session. In remote multi-user\ndeployments, an attacker can occupy a server worker thread indefinitely.\n\n### Suggested Fix\n\nThe preferred fix for the current git head is to use a linear-time regex engine for\nregex search mode while preserving literal matching behavior when regex mode is off.\n\nSuggested patch:\n\n```diff\ndiff --git a/builtins/pom.xml b/builtins/pom.xml\n--- a/builtins/pom.xml\n+++ b/builtins/pom.xml\n@@\n \u003cdependency\u003e\n+ \u003cgroupId\u003ecom.google.re2j\u003c/groupId\u003e\n+ \u003cartifactId\u003ere2j\u003c/artifactId\u003e\n+ \u003cversion\u003e1.8\u003c/version\u003e\n+ \u003c/dependency\u003e\n+ \u003cdependency\u003e\n \u003cgroupId\u003eorg.jline\u003c/groupId\u003e\n \u003cartifactId\u003ejline-reader\u003c/artifactId\u003e\n \u003c/dependency\u003e\n\ndiff --git a/builtins/src/main/java/org/jline/builtins/Nano.java b/builtins/src/main/java/org/jline/builtins/Nano.java\n--- a/builtins/src/main/java/org/jline/builtins/Nano.java\n+++ b/builtins/src/main/java/org/jline/builtins/Nano.java\n@@\n-import java.util.regex.Pattern;\n+import com.google.re2j.Pattern;\n```\n\nIf a dependency change is not acceptable, a fallback mitigation is to reject dangerous\nregex constructs or execute regex matching with a strict timeout, but that is weaker\nthan replacing the backtracking engine.\n\n### Credits\n\nThis issue was identified by Micha\u0142 Majchrowicz and Marcin Wyczechowski, members of the AFINE Team.",
"id": "GHSA-ph9c-7hw9-vhhw",
"modified": "2026-09-23T18:12:38Z",
"published": "2026-09-23T18:12:38Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/jline/jline3/security/advisories/GHSA-ph9c-7hw9-vhhw"
},
{
"type": "WEB",
"url": "https://github.com/jline/jline3/pull/2012"
},
{
"type": "WEB",
"url": "https://github.com/jline/jline3/pull/2018"
},
{
"type": "WEB",
"url": "https://github.com/jline/jline3/commit/1d5fc3099e77938b971e197211cad2d4fbb17541"
},
{
"type": "WEB",
"url": "https://github.com/jline/jline3/commit/341ee69ccc57b7733c1b40d6993219b64b3206ae"
},
{
"type": "PACKAGE",
"url": "https://github.com/jline/jline3"
},
{
"type": "WEB",
"url": "https://github.com/jline/jline3/releases/tag/4.3.1"
},
{
"type": "WEB",
"url": "https://github.com/jline/jline3/releases/tag/jline-3.30.15"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
],
"summary": "JLine: ReDoS in Nano Editor Regex Search Mode"
}
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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