CVE-2026-34480
Apache Log4j Core: Silent log event loss in XmlLayout due to unescaped XML 1.0 forbidden characters
At a glance
- Source
- NVD
- EPSS
- EPSS 1.05 % · percentile 64 ()
- State
- PUBLISHED
- Published
- Updated
- Assigner
- apache
- NVD status
- Analyzed
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.
Weaknesses (CWE)
- CWE-116 — Improper Encoding or Escaping of Output
References
- https://github.com/apache/logging-log4j2/pull/4077
- https://logging.apache.org/security.html#CVE-2026-34480
- https://logging.apache.org/cyclonedx/vdr.xml
- https://logging.apache.org/log4j/2.x/manual/layouts.html#XmlLayout
- https://lists.apache.org/thread/5x0hcnng0chhghp6jgjdp3qmbbhfjzhb
- http://www.openwall.com/lists/oss-security/2026/04/10/9
Scores
| Version | Score | Vector | Scored by |
|---|---|---|---|
| CVSS 4.0 | MEDIUM 6.9 | 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 | apache |
| CVSS 4.0 | MEDIUM 6.9 | 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 | NVD · security@apache.org (Secondary) |
| CVSS 3.1 | HIGH 7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N | NVD · nvd@nist.gov (Primary) |
Advisories
- GHSA-3pxv-7cmr-fjr4 — Apache Log4j Core: Silent log event loss in XmlLayout due to unescaped XML 1.0 forbidden characters
European references
- ENISA EUVD · EUVD-2026-21410
- GCVE · GCVE-0-2026-34480
CERT-FR advisories
- CERTFR-2026-AVI-1385 — Multiples vulnérabilités dans les produits VMware · cert.ssi.gouv.fr
- CERTFR-2026-AVI-1256 — Multiples vulnérabilités dans les produits IBM · cert.ssi.gouv.fr
- CERTFR-2026-AVI-1206 — Multiples vulnérabilités dans les produits IBM · cert.ssi.gouv.fr
- CERTFR-2026-AVI-1165 — Multiples vulnérabilités dans les produits IBM · cert.ssi.gouv.fr
- CERTFR-2026-AVI-1121 — Multiples vulnérabilités dans les produits IBM · cert.ssi.gouv.fr
- CERTFR-2026-AVI-1049 — Multiples vulnérabilités dans Oracle MySQL · cert.ssi.gouv.fr
- CERTFR-2026-AVI-1032 — Multiples vulnérabilités dans les produits IBM · cert.ssi.gouv.fr
- CERTFR-2026-AVI-0998 — Multiples vulnérabilités dans les produits SAP · cert.ssi.gouv.fr
- CERTFR-2026-AVI-0986 — Multiples vulnérabilités dans les produits IBM · cert.ssi.gouv.fr
- CERTFR-2026-AVI-0958 — Multiples vulnérabilités dans les produits IBM · cert.ssi.gouv.fr
- CERTFR-2026-AVI-0920 — Multiples vulnérabilités dans Oracle Weblogic · cert.ssi.gouv.fr
- CERTFR-2026-AVI-0810 — Multiples vulnérabilités dans les produits IBM · cert.ssi.gouv.fr
- CERTFR-2026-AVI-0736 — Multiples vulnérabilités dans les produits Splunk · cert.ssi.gouv.fr
- CERTFR-2026-AVI-0698 — Multiples vulnérabilités dans les produits IBM · cert.ssi.gouv.fr
- CERTFR-2026-AVI-0627 — Multiples vulnérabilités dans les produits Splunk · cert.ssi.gouv.fr
- CERTFR-2026-AVI-0500 — Multiples vulnérabilités dans VMware Tanzu · cert.ssi.gouv.fr
Affected configurations (NVD CPE)
cpe:2.3:a:apache:log4j:*:*:*:*:*:*:*:*≥ 2.0 < 2.25.4cpe:2.3:a:apache:log4j:3.0.0:alpha1:*:*:*:*:*:*cpe:2.3:a:apache:log4j:3.0.0:alpha1_rc1:*:*:*:*:*:*cpe:2.3:a:apache:log4j:3.0.0:alpha1_rc2:*:*:*:*:*:*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:*:*:*:*:*:*
Affected products
| Product | Versions |
|---|---|
| Apache Software Foundation · Apache Log4j Core | affected 2.0-alpha1 < 2.25.4 ; affected 3.0.0-alpha1 ≤ 3.0.0-beta3 |
Sources
| Source | Licence |
|---|---|
| CVE List (CVEProject cvelistV5) | CVE Program Terms of Use |
| EPSS (FIRST.org) | FIRST — attribution requested |
| ENISA EUVD | ENISA — reproduction authorised, source acknowledged |
| CERT-FR (ANSSI) | Licence Ouverte / Etalab 2.0 |
| NVD (NIST) via fkie-cad/nvd-json-data-feeds | Public domain — this product uses data from the NVD API but is not endorsed or certified by the NVD |