CVE-2026-40023

#include <log4cxx/xml/xmllayout.h> #include <log4cxx/fileappender.h> #include <log4cxx/logger.h> using namespace log4cxx; void demonstrate_poc() { LoggerPtr logger(Logger::getLogger("ExploitLogger")); LayoutPtr layout(new xml::XMLLayout()); AppenderPtr appender(new FileAppender(layout, "output.xml")); logger->addAppender(appender); // Attack vector: Injecting a forbidden XML 1.0 character (e.g., NULL byte) // This causes the XML output to be malformed and parsers to reject it. std::string maliciousPayload = "User login: admin\x00"; // 0x00 is illegal in XML 1.0 LOG4CXX_INFO(logger, maliciousPayload); }

{"cve": {"id": "CVE-2026-40023", "sourceIdentifier": "[email protected]", "published": "2026-04-10T16:16:32.600", "lastModified": "2026-04-21T14:49:42.767", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "Apache Log4cxx's XMLLayout https://logging.apache.org/log4cxx/1.7.0/classlog4cxx_1_1xml_1_1XMLLayout.html , in versions before 1.7.0, fails to sanitize characters forbidden by the XML 1.0 specification https://www.w3.org/TR/xml/#charsets in log messages, NDC, and MDC property keys and values, producing invalid XML output. Conforming XML parsers must reject such documents with a fatal error, which may cause downstream log processing systems to drop or fail to index affected records.\n\nAn attacker who can influence logged data can exploit this to suppress individual log records, impairing audit trails and detection of malicious activity.\n\nUsers are advised to upgrade to Apache Log4cxx 1.7.0, which fixes this issue."}], "metrics": {"cvssMetricV40": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "4.0", "vectorString": "CVSS:4.0/AV:N/AC:H/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": 6.3, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "HIGH", "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:L/A:N", "baseScore": 5.3, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "LOW", "availabilityImpact": "NONE"}, "exploitabilityScore": 3.9, "impactScore": 1.4}]}, "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:log4cxx:*:*:*:*:*:*:*:*", "versionEndExcluding": "1.7.0", "matchCriteriaId": "8ACE57FE-D5F6-4875-976B-7EFADC4F714A"}]}]}], "references": [{"url": "https://github.com/apache/logging-log4cxx/pull/609", "source": "[email protected]", "tags": ["Issue Tracking", "Patch"]}, {"url": "https://lists.apache.org/thread/y15cv3zblg3dfwr5vy6ddbnl4zyrzr8b", "source": "[email protected]", "tags": ["Mailing List", "Vendor Advisory"]}, {"url": "https://logging.apache.org/cyclonedx/vdr.xml", "source": "[email protected]", "tags": ["Product"]}, {"url": "https://logging.apache.org/log4cxx/1.7.0/classlog4cxx_1_1xml_1_1XMLLayout.html", "source": "[email protected]", "tags": ["Product"]}, {"url": "https://logging.apache.org/security.html#CVE-2026-40023", "source": "[email protected]", "tags": ["Vendor Advisory"]}, {"url": "http://www.openwall.com/lists/oss-security/2026/04/10/12", "source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Mailing List", "Third Party Advisory"]}]}}