CVE-2026-77421: JLine Denial of Service Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-ph9c-7hw9-vhhw",
  "modified" : "2026-09-23T18:12:38Z",
  "published" : "2026-09-23T18:12:38Z",
  "aliases" : [ "CVE-2026-77421" ],
  "summary" : "JLine: ReDoS in Nano Editor Regex Search Mode",
  "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's 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's 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         <dependency>\n+            <groupId>com.google.re2j</groupId>\n+            <artifactId>re2j</artifactId>\n+            <version>1.8</version>\n+        </dependency>\n+        <dependency>\n             <groupId>org.jline</groupId>\n             <artifactId>jline-reader</artifactId>\n         </dependency>\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 Michał Majchrowicz and Marcin Wyczechowski, members of the AFINE Team.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.jline:jline-builtins"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.0.0"
      }, {
        "fixed" : "4.3.1"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.jline:jline-builtins"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "3.0.0"
      }, {
        "fixed" : "3.30.15"
      } ]
    } ]
  } ],
  "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"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1333" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-23T18:12:38Z",
    "nvd_published_at" : null
  }
}