{
    "dataType": "CVE_RECORD",
    "dataVersion": "5.2",
    "cveMetadata": {
        "cveId": "CVE-2026-34479",
        "assignerOrgId": "f0158376-9dc2-43b6-827c-5f631a4d8d09",
        "state": "PUBLISHED",
        "assignerShortName": "apache",
        "dateReserved": "2026-03-28T14:06:31.965Z",
        "datePublished": "2026-04-10T15:41:07.888Z",
        "dateUpdated": "2026-04-10T17:47:34.402Z"
    },
    "containers": {
        "cna": {
            "affected": [
                {
                    "collectionURL": "https://repo.maven.apache.org/maven2",
                    "cpes": [
                        "cpe:2.3:a:apache:log4j_1_2_api:*:*:*:*:*:*:*:*"
                    ],
                    "defaultStatus": "unaffected",
                    "packageName": "org.apache.logging.log4j:log4j-1.2-api",
                    "packageURL": "pkg:maven/org.apache.logging.log4j/log4j-1.2-api",
                    "product": "Apache Log4j 1 to Log4j 2 bridge",
                    "vendor": "Apache Software Foundation",
                    "versions": [
                        {
                            "lessThan": "2.25.4",
                            "status": "affected",
                            "version": "2.7",
                            "versionType": "maven"
                        },
                        {
                            "lessThanOrEqual": "3.0.0-beta2",
                            "status": "affected",
                            "version": "3.0.0-alpha1",
                            "versionType": "maven"
                        }
                    ]
                }
            ],
            "credits": [
                {
                    "lang": "en",
                    "type": "finder",
                    "value": "Ap4sh (Samy Medjahed) and Ethicxz (Eliott Laurie) (original reporters)"
                },
                {
                    "lang": "en",
                    "type": "finder",
                    "value": "jabaltarik1 (independently)"
                }
            ],
            "descriptions": [
                {
                    "lang": "en",
                    "supportingMedia": [
                        {
                            "base64": false,
                            "type": "text/html",
                            "value": "<p>The <code>Log4j1XmlLayout</code> 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.</p><p>Two groups of users are affected:</p><ul><li>Those using <code>Log4j1XmlLayout</code> directly in a Log4j Core 2 configuration file.</li><li>Those using the Log4j 1 configuration compatibility layer with <code>org.apache.log4j.xml.XMLLayout</code> specified as the layout class.</li></ul><p>Users are advised to upgrade to Apache Log4j 1-to-Log4j 2 bridge version 2.25.4, which corrects this issue.</p><p><strong>Note:</strong> The Apache Log4j 1-to-Log4j 2 bridge is deprecated and will not be present in Log4j 3. Users are encouraged to consult the <a target=\"_blank\" rel=\"nofollow\" href=\"https://logging.apache.org/log4j/2.x/migrate-from-log4j1.html\">Log4j 1 to Log4j 2 migration guide</a>, and specifically the section on eliminating reliance on the bridge.</p>"
                        }
                    ],
                    "value": "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\n\nUsers are advised to upgrade to Apache Log4j 1-to-Log4j 2 bridge version 2.25.4, which corrects this issue.\n\nNote: 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 https://logging.apache.org/log4j/2.x/migrate-from-log4j1.html , and specifically the section on eliminating reliance on the bridge."
                }
            ],
            "metrics": [
                {
                    "cvssV4_0": {
                        "Automatable": "NOT_DEFINED",
                        "Recovery": "NOT_DEFINED",
                        "Safety": "NOT_DEFINED",
                        "attackComplexity": "LOW",
                        "attackRequirements": "NONE",
                        "attackVector": "NETWORK",
                        "baseScore": 6.9,
                        "baseSeverity": "MEDIUM",
                        "privilegesRequired": "NONE",
                        "providerUrgency": "NOT_DEFINED",
                        "subAvailabilityImpact": "NONE",
                        "subConfidentialityImpact": "NONE",
                        "subIntegrityImpact": "LOW",
                        "userInteraction": "NONE",
                        "valueDensity": "NOT_DEFINED",
                        "vectorString": "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",
                        "version": "4.0",
                        "vulnAvailabilityImpact": "NONE",
                        "vulnConfidentialityImpact": "NONE",
                        "vulnIntegrityImpact": "NONE",
                        "vulnerabilityResponseEffort": "NOT_DEFINED"
                    },
                    "format": "CVSS",
                    "scenarios": [
                        {
                            "lang": "en",
                            "value": "GENERAL"
                        }
                    ]
                },
                {
                    "other": {
                        "content": {
                            "text": "moderate"
                        },
                        "type": "Textual description of severity"
                    }
                }
            ],
            "problemTypes": [
                {
                    "descriptions": [
                        {
                            "cweId": "CWE-116",
                            "description": "CWE-116 Improper Encoding or Escaping of Output",
                            "lang": "en",
                            "type": "CWE"
                        }
                    ]
                }
            ],
            "providerMetadata": {
                "orgId": "f0158376-9dc2-43b6-827c-5f631a4d8d09",
                "shortName": "apache",
                "dateUpdated": "2026-04-10T15:41:07.888Z"
            },
            "references": [
                {
                    "tags": [
                        "patch"
                    ],
                    "url": "https://github.com/apache/logging-log4j2/pull/4078"
                },
                {
                    "tags": [
                        "vendor-advisory"
                    ],
                    "url": "https://logging.apache.org/security.html#CVE-2026-34479"
                },
                {
                    "tags": [
                        "vendor-advisory"
                    ],
                    "url": "https://logging.apache.org/cyclonedx/vdr.xml"
                },
                {
                    "tags": [
                        "related"
                    ],
                    "url": "https://logging.apache.org/log4j/2.x/migrate-from-log4j1.html"
                },
                {
                    "tags": [
                        "vendor-advisory"
                    ],
                    "url": "https://lists.apache.org/thread/gd0hp6mj17rn3kj279vgy4p7kd4zz5on"
                }
            ],
            "source": {
                "discovery": "EXTERNAL"
            },
            "timeline": [
                {
                    "lang": "en",
                    "time": "2026-02-16T17:11:00.000Z",
                    "value": "Vulnerability reported by Ap4sh and ethicxz"
                },
                {
                    "lang": "en",
                    "time": "2026-03-15T05:39:00.000Z",
                    "value": "Independent report received from jabaltarik1"
                },
                {
                    "lang": "en",
                    "time": "2026-03-24T18:56:00.000Z",
                    "value": "Fix shared publicly by Piotr P. Karwasz as pull request #4078"
                },
                {
                    "lang": "en",
                    "time": "2026-03-25T09:46:00.000Z",
                    "value": "Fix verified by reporter"
                },
                {
                    "lang": "en",
                    "time": "2026-03-28T11:19:00.000Z",
                    "value": "Log4j 2.25.4 released"
                }
            ],
            "title": "Apache Log4j 1 to Log4j 2 bridge: Silent log event loss in Log4j1XmlLayout due to unescaped XML 1.0 forbidden characters",
            "x_generator": {
                "engine": "Vulnogram 0.2.0"
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        },
        "adp": [
            {
                "title": "CVE Program Container",
                "references": [
                    {
                        "url": "http://www.openwall.com/lists/oss-security/2026/04/10/8"
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                ],
                "providerMetadata": {
                    "orgId": "af854a3a-2127-422b-91ae-364da2661108",
                    "shortName": "CVE",
                    "dateUpdated": "2026-04-10T16:18:18.699Z"
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            {
                "metrics": [
                    {
                        "other": {
                            "type": "ssvc",
                            "content": {
                                "timestamp": "2026-04-10T17:45:24.466114Z",
                                "id": "CVE-2026-34479",
                                "options": [
                                    {
                                        "Exploitation": "none"
                                    },
                                    {
                                        "Automatable": "yes"
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                                        "Technical Impact": "partial"
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                                "role": "CISA Coordinator",
                                "version": "2.0.3"
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                "title": "CISA ADP Vulnrichment",
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                    "shortName": "CISA-ADP",
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