CVE-2026-34480
Description
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.
Predictions
Heuristic predictions, AS-IS, for prioritization only.
Mitigations
No mitigations published for this CVE yet.
The vendor-content worker queues fetches as references arrive (check back in a few minutes). Or — if you've already worked around this in production — publish your fix to the community-verified tier.
✚ Propose a mitigation on Community → Mitigations published via the community go through AI scoring + 2 human reviewers + 7-day silent objection window before landing here withsource_tier=community-verified.
OS impact
Debian Affected 5 releases
| Version | Status | Fixed in |
|---|---|---|
| trixie | Affected | — |
| sid | Affected | — |
| forky | Affected | — |
| bullseye | Affected | — |
| bookworm | Affected | — |
SUSE Affected 1 release
| Version | Status | Fixed in |
|---|---|---|
| — | Affected | — |
Package impact
| Ecosystem | Package | Vulnerable | Fixed |
|---|---|---|---|
| Maven | org.apache.logging.log4j:log4j-core | >=2.0-alpha1,<2.25.4 | 2.25.4 |
| Maven | org.apache.logging.log4j:log4j-core | >=3.0.0-alpha1,<=3.0.0-beta3 | |
Application impact
| Vendor | Product | Versions | Fixed |
|---|---|---|---|
| gcp | | |
References
- https://security-tracker.debian.org/tracker/CVE-2026-34480
- https://nvd.nist.gov/vuln/detail/CVE-2026-34480
- https://github.com/apache/logging-log4j2/pull/4077
- https://github.com/apache/logging-log4j2
- https://lists.apache.org/thread/5x0hcnng0chhghp6jgjdp3qmbbhfjzhb
- https://logging.apache.org/cyclonedx/vdr.xml
- https://logging.apache.org/log4j/2.x/manual/layouts.html#XmlLayout
- https://logging.apache.org/security.html#CVE-2026-34480
- http://www.openwall.com/lists/oss-security/2026/04/10/9
- https://www.suse.com/security/cve/CVE-2026-34480.html
Community-verified mitigations for this CVE will appear above when contributors publish them.
Verify integrity in audit chain (admin only). AS-IS.