CVE-2026-77420: JLine Denial of Service Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-5q95-hrpc-m3w3",
  "modified" : "2026-09-23T18:12:06Z",
  "published" : "2026-09-23T18:12:05Z",
  "aliases" : [ "CVE-2026-77420" ],
  "summary" : "JLine: ReDoS via `HISTORY_IGNORE` Configuration Variable",
  "details" : "### Summary\n\nThe JLine3 `HISTORY_IGNORE` variable is converted into a Java regular expression with\nonly partial escaping. As a result, regex metacharacters other than `*` and `:` are\npassed through to the regex engine. A crafted value such as `(a+)+b` can cause\ncatastrophic backtracking each time a command line is added to history, hanging the\nreader thread at high CPU.\n\n### Details\n\nIn `reader/src/main/java/org/jline/reader/impl/history/DefaultHistory.java`,\n`matchPatterns()` converts `HISTORY_IGNORE` into a regex:\n\n```java\nfor (int i = 0; i < patterns.length(); i++) {\n    char ch = patterns.charAt(i);\n    if (ch == '\\\\') {\n        ch = patterns.charAt(++i);\n        sb.append(ch);\n    } else if (ch == ':') {\n        sb.append('|');\n    } else if (ch == '*') {\n        sb.append('.').append('*');\n    } else {\n        sb.append(ch);\n    }\n}\nreturn line.matches(sb.toString());\n```\n\nThis logic translates wildcard syntax but does not escape regex metacharacters such as\n`(`, `)`, `+`, `?`, `{`, `}`, `[`, and `]`. Those characters therefore reach the Java\nregex engine unchanged.\n\nAffected source location:\n- `reader/src/main/java/org/jline/reader/impl/history/DefaultHistory.java`\n- `matchPatterns(String patterns, String line)`\n\n### PoC\n\n1. Configure `HISTORY_IGNORE` to a malicious pattern, for example:\n\n```sh\nset history-ignore \"(a+)+b\"\n```\n\n2. At the JLine prompt, enter a long non-matching line:\n\n```text\naaaaaaaaaaaaaaaaaaaaaaaaaaax\n```\n\n3. Press Enter.\n\nExpected result:\n- The prompt does not return.\n- The reader 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-reader` are impacted if they allow\n`HISTORY_IGNORE` to be configured through user configuration or application settings.\nThe issue is lower severity than the interactive editor findings because the attacker\nmust control configuration, but it can still reliably hang a reader session.\n\n### Suggested Fix\n\nThe safest fix for the current git head is to stop treating arbitrary `HISTORY_IGNORE`\ncontent as a regex. Instead, escape all characters by default and translate only the\nintended JLine wildcard syntax (`*`) and separator syntax (`:`).\n\nSuggested patch:\n\n```diff\ndiff --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\n--- a/reader/src/main/java/org/jline/reader/impl/history/DefaultHistory.java\n+++ b/reader/src/main/java/org/jline/reader/impl/history/DefaultHistory.java\n@@\n         StringBuilder sb = new StringBuilder();\n         for (int i = 0; i < patterns.length(); i++) {\n             char ch = patterns.charAt(i);\n             if (ch == '\\\\') {\n                 ch = patterns.charAt(++i);\n-                sb.append(ch);\n+                sb.append(Pattern.quote(Character.toString(ch)));\n             } else if (ch == ':') {\n                 sb.append('|');\n             } else if (ch == '*') {\n                 sb.append('.').append('*');\n             } else {\n-                sb.append(ch);\n+                sb.append(Pattern.quote(Character.toString(ch)));\n             }\n         }\n         return line.matches(sb.toString());\n```\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:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.jline:jline-reader"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.0.0"
      }, {
        "fixed" : "4.3.1"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.jline:jline-reader"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "3.0.0"
      }, {
        "fixed" : "3.30.15"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/jline/jline3/security/advisories/GHSA-5q95-hrpc-m3w3"
  }, {
    "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" : "2026-09-23T18:12:05Z",
    "nvd_published_at" : null
  }
}