GHSA-H383-GMXW-35V2

Vulnerability from github – Published: 2026-04-10 18:31 – Updated: 2026-04-14 00:10
VLAI
Summary
Apache Log4j 1 to Log4j 2 bridge: silent log event loss in Log4j1XmlLayout due to unescaped XML 1.0 forbidden characters
Details

The Log4j1XmlLayout from the Apache Log4j 1-to-Log4j 2 bridge fails to escape characters forbidden by the XML 1.0 standard, producing malformed XML output. Conforming XML parsers are required to reject documents containing such characters with a fatal error, which may cause downstream log processing systems to drop or fail to index affected records.

Two groups of users are affected:

  • Those using Log4j1XmlLayout directly in a Log4j Core 2 configuration file.
  • Those using the Log4j 1 configuration compatibility layer with org.apache.log4j.xml.XMLLayout specified as the layout class.

Users are advised to upgrade to Apache Log4j 1-to-Log4j 2 bridge version 2.25.4, which corrects this issue.

[!NOTE] The Apache Log4j 1-to-Log4j 2 bridge is deprecated and will not be present in Log4j 3. Users are encouraged to consult the Log4j 1 to Log4j 2 migration guide, and specifically the section on eliminating reliance on the bridge.

Severity
6.9 (Medium)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N
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{
  "affected": [
    {
      "package": {
        "ecosystem": "Maven",
        "name": "org.apache.logging.log4j:log4j-1.2-api"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.7"
            },
            {
              "fixed": "2.25.4"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Maven",
        "name": "org.apache.logging.log4j:log4j-1.2-api"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.0.0-beta1"
            },
            {
              "last_affected": "3.0.0-beta2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-34479"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-116"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-04-14T00:10:59Z",
    "nvd_published_at": "2026-04-10T16:16:31Z",
    "severity": "MODERATE"
  },
  "details": "The `Log4j1XmlLayout` from the Apache Log4j 1-to-Log4j 2 bridge fails to escape characters forbidden by the XML 1.0 standard, producing malformed XML output. Conforming XML parsers are required to reject documents containing such characters with a fatal error, which may cause downstream log processing systems to drop or fail to index affected records.\n\nTwo groups of users are affected:\n\n* Those using `Log4j1XmlLayout` directly in a Log4j Core 2 configuration file.\n* Those using the Log4j 1 configuration compatibility layer with `org.apache.log4j.xml.XMLLayout` specified as the layout class.\n\nUsers are advised to upgrade to Apache Log4j 1-to-Log4j 2 bridge version `2.25.4`, which corrects this issue.\n\n\u003e [!NOTE]\n\u003e The Apache Log4j 1-to-Log4j 2 bridge is deprecated and will not be present in Log4j 3. Users are encouraged to consult the\n\u003e [Log4j 1 to Log4j 2 migration guide](https://logging.apache.org/log4j/2.x/migrate-from-log4j1.html), and specifically the section on eliminating reliance on the bridge.",
  "id": "GHSA-h383-gmxw-35v2",
  "modified": "2026-04-14T00:10:59Z",
  "published": "2026-04-10T18:31:18Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-34479"
    },
    {
      "type": "WEB",
      "url": "https://github.com/apache/logging-log4j2/pull/4078"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/apache/logging-log4j2"
    },
    {
      "type": "WEB",
      "url": "https://lists.apache.org/thread/gd0hp6mj17rn3kj279vgy4p7kd4zz5on"
    },
    {
      "type": "WEB",
      "url": "https://logging.apache.org/cyclonedx/vdr.xml"
    },
    {
      "type": "WEB",
      "url": "https://logging.apache.org/log4j/2.x/migrate-from-log4j1.html"
    },
    {
      "type": "WEB",
      "url": "https://logging.apache.org/security.html#CVE-2026-34479"
    },
    {
      "type": "WEB",
      "url": "http://www.openwall.com/lists/oss-security/2026/04/10/8"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Apache Log4j 1 to Log4j 2 bridge: silent log event loss in Log4j1XmlLayout due to unescaped XML 1.0 forbidden characters"
}



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