{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-34479","assignerOrgId":"f0158376-9dc2-43b6-827c-5f631a4d8d09","state":"PUBLISHED","assignerShortName":"apache","dateReserved":"2026-03-28T14:06:31.965Z","datePublished":"2026-04-10T15:41:07.888Z","dateUpdated":"2026-04-10T17:47:34.402Z"},"containers":{"cna":{"affected":[{"collectionURL":"https://repo.maven.apache.org/maven2","cpes":["cpe:2.3:a:apache:log4j_1_2_api:*:*:*:*:*:*:*:*"],"defaultStatus":"unaffected","packageName":"org.apache.logging.log4j:log4j-1.2-api","packageURL":"pkg:maven/org.apache.logging.log4j/log4j-1.2-api","product":"Apache Log4j 1 to Log4j 2 bridge","vendor":"Apache Software Foundation","versions":[{"lessThan":"2.25.4","status":"affected","version":"2.7","versionType":"maven"},{"lessThanOrEqual":"3.0.0-beta2","status":"affected","version":"3.0.0-alpha1","versionType":"maven"}]}],"credits":[{"lang":"en","type":"finder","value":"Ap4sh (Samy Medjahed) and Ethicxz (Eliott Laurie) (original reporters)"},{"lang":"en","type":"finder","value":"jabaltarik1 (independently)"}],"descriptions":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","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.

Two groups of users are affected:

Users are advised to upgrade to Apache Log4j 1-to-Log4j 2 bridge version 2.25.4, which corrects this issue.

Note: 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, and specifically the section on eliminating reliance on the bridge.

"}],"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":[{"cvssV4_0":{"Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","Safety":"NOT_DEFINED","attackComplexity":"LOW","attackRequirements":"NONE","attackVector":"NETWORK","baseScore":6.9,"baseSeverity":"MEDIUM","privilegesRequired":"NONE","providerUrgency":"NOT_DEFINED","subAvailabilityImpact":"NONE","subConfidentialityImpact":"NONE","subIntegrityImpact":"LOW","userInteraction":"NONE","valueDensity":"NOT_DEFINED","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","version":"4.0","vulnAvailabilityImpact":"NONE","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"NONE","vulnerabilityResponseEffort":"NOT_DEFINED"},"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}]},{"other":{"content":{"text":"moderate"},"type":"Textual description of severity"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-116","description":"CWE-116 Improper Encoding or Escaping of Output","lang":"en","type":"CWE"}]}],"providerMetadata":{"orgId":"f0158376-9dc2-43b6-827c-5f631a4d8d09","shortName":"apache","dateUpdated":"2026-04-10T15:41:07.888Z"},"references":[{"tags":["patch"],"url":"https://github.com/apache/logging-log4j2/pull/4078"},{"tags":["vendor-advisory"],"url":"https://logging.apache.org/security.html#CVE-2026-34479"},{"tags":["vendor-advisory"],"url":"https://logging.apache.org/cyclonedx/vdr.xml"},{"tags":["related"],"url":"https://logging.apache.org/log4j/2.x/migrate-from-log4j1.html"},{"tags":["vendor-advisory"],"url":"https://lists.apache.org/thread/gd0hp6mj17rn3kj279vgy4p7kd4zz5on"}],"source":{"discovery":"EXTERNAL"},"timeline":[{"lang":"en","time":"2026-02-16T17:11:00.000Z","value":"Vulnerability reported by Ap4sh and ethicxz"},{"lang":"en","time":"2026-03-15T05:39:00.000Z","value":"Independent report received from jabaltarik1"},{"lang":"en","time":"2026-03-24T18:56:00.000Z","value":"Fix shared publicly by Piotr P. Karwasz as pull request #4078"},{"lang":"en","time":"2026-03-25T09:46:00.000Z","value":"Fix verified by reporter"},{"lang":"en","time":"2026-03-28T11:19:00.000Z","value":"Log4j 2.25.4 released"}],"title":"Apache Log4j 1 to Log4j 2 bridge: Silent log event loss in Log4j1XmlLayout due to unescaped XML 1.0 forbidden characters","x_generator":{"engine":"Vulnogram 0.2.0"}},"adp":[{"title":"CVE Program Container","references":[{"url":"http://www.openwall.com/lists/oss-security/2026/04/10/8"}],"providerMetadata":{"orgId":"af854a3a-2127-422b-91ae-364da2661108","shortName":"CVE","dateUpdated":"2026-04-10T16:18:18.699Z"}},{"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-04-10T17:45:24.466114Z","id":"CVE-2026-34479","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"title":"CISA ADP Vulnrichment","providerMetadata":{"orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","shortName":"CISA-ADP","dateUpdated":"2026-04-10T17:47:34.402Z"}}]}}