CVE-2026-34480

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Source
https://cve.org/CVERecord?id=CVE-2026-34480
Import Source
https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-34480.json
JSON Data
https://api.osv.dev/v1/vulns/CVE-2026-34480
Aliases
Downstream
Related
Published
2026-04-10T15:42:03.843Z
Modified
2026-07-15T02:19:24.782537465Z
Severity
  • 6.9 (Medium) CVSS_V4 - 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 CVSS Calculator
Summary
Apache Log4j Core: Silent log event loss in XmlLayout due to unescaped XML 1.0 forbidden characters
Details

Apache Log4j Core's XmlLayout https://logging.apache.org/log4j/2.x/manual/layouts.html#XmlLayout , in versions up to and including 2.25.3, fails to sanitize characters forbidden by the XML 1.0 specification https://www.w3.org/TR/xml/#charsets producing invalid XML output whenever a log message or MDC value contains such characters.

The impact depends on the StAX implementation in use:

  • JRE built-in StAX: Forbidden characters are silently written to the output, producing malformed XML. Conforming parsers must reject such documents with a fatal error, which may cause downstream log-processing systems to drop the affected records.
  • Alternative StAX implementations (e.g., Woodstox https://github.com/FasterXML/woodstox , a transitive dependency of the Jackson XML Dataformat module): An exception is thrown during the logging call, and the log event is never delivered to its intended appender, only to Log4j's internal status logger.

Users are advised to upgrade to Apache Log4j Core 2.25.4, which corrects this issue by sanitizing forbidden characters before XML output.

Database specific 
{
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/34xxx/CVE-2026-34480.json",
    "cwe_ids": [
        "CWE-116"
    ],
    "cna_assigner": "apache"
}
References

Affected packages

Git / github.com/apache/logging-log4j2

Affected ranges

Type
GIT
Repo
https://github.com/apache/logging-log4j2
Events
Introduced
8d9204a4b4c6016fa6b36513a46502689d6a45c1
Fixed
0628e53b25a33e496b509c40a39f2d7c64f2aa6c
Introduced
e84827220de69f39112d5f518279038c152b186f
Last affected
28117e55f69892d3454672f9399e53fb7b74a321
Database specific 
{
    "cpe": [
        "cpe:2.3:a:apache:log4j:*:*:*:*:*:*:*:*",
        "cpe:2.3:a:apache:log4j:3.0.0:alpha1:*:*:*:*:*:*",
        "cpe:2.3:a:apache:log4j:3.0.0:beta1:*:*:*:*:*:*",
        "cpe:2.3:a:apache:log4j:3.0.0:beta2:*:*:*:*:*:*",
        "cpe:2.3:a:apache:log4j:3.0.0:beta3:*:*:*:*:*:*"
    ],
    "source": [
        "CPE_RANGE",
        "CPE_STRING"
    ],
    "extracted_events": [
        {
            "introduced": "2.0"
        },
        {
            "fixed": "2.25.4"
        },
        {
            "introduced": "3.0.0-alpha1"
        },
        {
            "last_affected": "3.0.0-alpha1"
        },
        {
            "introduced": "3.0.0-beta1"
        },
        {
            "last_affected": "3.0.0-beta1"
        },
        {
            "introduced": "3.0.0-beta2"
        },
        {
            "last_affected": "3.0.0-beta2"
        },
        {
            "introduced": "3.0.0-beta3"
        },
        {
            "last_affected": "3.0.0-beta3"
        }
    ]
}

Affected versions

3.*
3.0.0-alpha1
3.0.0-beta1
3.0.0-beta2
3.0.0-beta3
log4j-3.*
log4j-3.0.0-alpha1-rc2
rel/3.*
rel/3.0.0-alpha1
rel/3.0.0-beta3

Database specific

source 
"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-34480.json"