CVE-2026-34480 (GCVE-0-2026-34480)
Vulnerability from cvelistv5
Published
2026-04-10 15:42
Modified
2026-04-10 17:45
Severity ?
VLAI Severity ?
EPSS score ?
CWE
- CWE-116 - Improper Encoding or Escaping of Output
Summary
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.
References
| URL | Tags | |
|---|---|---|
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Impacted products
| Vendor | Product | Version | ||
|---|---|---|---|---|
| Apache Software Foundation | Apache Log4j Core |
Version: 2.0-alpha1 Version: 3.0.0-alpha1 cpe:2.3:a:apache:log4j:*:*:*:*:*:*:*:* |
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Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.
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