CVE-2026-34479

import org.apache.logging.log4j.LogManager; import org.apache.logging.log4j.Logger; public class CVE202634479PoC { private static final Logger logger = LogManager.getLogger(CVE202634479PoC.class); public static void main(String[] args) { // XML 1.0 forbidden character (e.g., NULL character) String maliciousPayload = "User input: \u0000"; // Log the payload using the vulnerable Log4j1XmlLayout // This will generate malformed XML causing parsing failures downstream logger.info("Processing request: {}", maliciousPayload); System.out.println("Log sent. Check downstream XML parser for fatal errors."); } }

{"cve": {"id": "CVE-2026-34479", "sourceIdentifier": "[email protected]", "published": "2026-04-10T16:16:31.270", "lastModified": "2026-05-06T18:21:34.373", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "The Log4j1XmlLayout from the Apache Log4j 1-to-Log4j 2 bridge fails to escape characters forbidden by the XML 1.0 standard, producing malformed XML output. Conforming XML parsers are required to reject documents containing such characters with a fatal error, which may cause downstream log processing systems to drop or fail to index affected records.\n\nTwo groups of users are affected:\n\n * Those using Log4j1XmlLayout directly in a Log4j Core 2 configuration file.\n * Those using the Log4j 1 configuration compatibility layer with org.apache.log4j.xml.XMLLayout specified as the layout class.\n\n\nUsers are advised to upgrade to Apache Log4j 1-to-Log4j 2 bridge version 2.25.4, which corrects this issue.\n\nNote: The Apache Log4j 1-to-Log4j 2 bridge is deprecated and will not be present in Log4j 3. Users are encouraged to consult the Log4j 1 to Log4j 2 migration guide https://logging.apache.org/log4j/2.x/migrate-from-log4j1.html , and specifically the section on eliminating reliance on the bridge."}], "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": "2.7", "versionEndExcluding": "2.25.4", "matchCriteriaId": "4D7C1729-01D6-4981-B3FB-3A877083AE28"}, {"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"}]}]}], "references": [{"url": "https://github.com/apache/logging-log4j2/pull/4078", "source": "[email protected]", "tags": ["Exploit", "Issue Tracking", "Patch"]}, {"url": "https://lists.apache.org/thread/gd0hp6mj17rn3kj279vgy4p7kd4zz5on", "source": "[email protected]", "tags": ["Mailing List"]}, {"url": "https://logging.apache.org/cyclonedx/vdr.xml", "source": "[email protected]", "tags": ["Vendor Advisory"]}, {"url": "https://logging.apache.org/log4j/2.x/migrate-from-log4j1.html", "source": "[email protected]", "tags": ["Mitigation"]}, {"url": "https://logging.a ... 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