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[GHSA-h383-gmxw-35v2] The Log4j1XmlLayout from the Apache Log4j 1-to-Log4j 2... #7358

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[GHSA-h383-gmxw-35v2] The Log4j1XmlLayout from the Apache Log4j 1-to-Log4j 2... #7358

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52 changes: 48 additions & 4 deletions advisories/unreviewed/2026/04/GHSA-h383-gmxw-35v2/GHSA-h383-gmxw-35v2.json
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Original file line number Diff line number Diff line change
@@ -1,19 +1,59 @@
{
"schema_version": "1.4.0",
"id": "GHSA-h383-gmxw-35v2",
"modified": "2026-04-10T18:31:18Z",
"modified": "2026-04-10T18:31:27Z",
"published": "2026-04-10T18:31:18Z",
"aliases": [
"CVE-2026-34479"
],
"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\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.",
"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.\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> [!NOTE]\n> 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[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.",
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The NOTE blockquote/admonition formatting is inconsistent: the line with the migration guide link is not part of the blockquote, so the “NOTE” may render oddly depending on the markdown renderer. If you want this to be a single note, prefix the link line with "> " (or avoid the GitHub-specific "[!NOTE]" admonition syntax and use plain text that renders consistently across consumers).

Suggested change
"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> [!NOTE]\n> 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[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.",
"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> [!NOTE]\n> 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> [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.",

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@ppkarwasz ppkarwasz Apr 10, 2026

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The suggestion sounds reasonable and should probably be merged (I don't have permission to do it).

"severity": [
{
"type": "CVSS_V4",
"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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X"
"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"
}
],
"affected": [
{
"package": {
"ecosystem": "Maven",
"name": "org.apache.logging.log4j:log4j-1.2-api"
},
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "2.7"
},
{
"fixed": "2.25.4"
}
]
}
]
},
{
"package": {
"ecosystem": "Maven",
"name": "org.apache.logging.log4j:log4j-1.2-api"
},
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "3.0.0-beta1"
},
{
"last_affected": "3.0.0-beta2"
}
]
}
]
}
],
"affected": [],
"references": [
{
"type": "ADVISORY",
Expand All @@ -23,6 +63,10 @@
"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"
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