CVE-2026-34477 (GCVE-0-2026-34477)

Vulnerability from cvelistv5 – Published: 2026-04-10 15:36 – Updated: 2026-04-10 17:38
VLAI
Title
Apache Log4j Core: verifyHostName attribute silently ignored in TLS configuration, allowing hostname verification bypass
Summary
The fix for CVE-2025-68161 https://logging.apache.org/security.html#CVE-2025-68161 was incomplete: it addressed hostname verification only when enabled via the log4j2.sslVerifyHostName https://logging.apache.org/log4j/2.x/manual/systemproperties.html#log4j2.sslVerifyHostName system property, but not when configured through the verifyHostName https://logging.apache.org/log4j/2.x/manual/appenders/network.html#SslConfiguration-attr-verifyHostName attribute of the <Ssl> element. Although the verifyHostName configuration attribute was introduced in Log4j Core 2.12.0, it was silently ignored in all versions through 2.25.3, leaving TLS connections vulnerable to interception regardless of the configured value. A network-based attacker may be able to perform a man-in-the-middle attack when all of the following conditions are met: * An SMTP, Socket, or Syslog appender is in use. * TLS is configured via a nested <Ssl> element. * The attacker can present a certificate issued by a CA trusted by the appender's configured trust store, or by the default Java trust store if none is configured. This issue does not affect users of the HTTP appender, which uses a separate verifyHostname https://logging.apache.org/log4j/2.x/manual/appenders/network.html#HttpAppender-attr-verifyHostName attribute that was not subject to this bug and verifies host names by default. Users are advised to upgrade to Apache Log4j Core 2.25.4, which corrects this issue.
Severity
6.3 (Medium)
CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:L/SA:N
CWE
  • CWE-297 - Improper Validation of Certificate with Host Mismatch
Assigner
References
Impacted products
Vendor Product Version
Apache Software Foundation Apache Log4j Core Affected: 2.12.0 , < 2.25.4 (maven)
Affected: 3.0.0-alpha1 , ≤ 3.0.0-beta3 (maven)
    cpe:2.3:a:apache:log4j:*:*:*:*:*:*:*:*
 Create a notification for this product.
Credits
Samuli Leinonen (original reporter) Naresh Kandula (independently) Vitaly Simonovich (independently) Raijuna (independently) Danish Siddiqui (djvirus, independently) Markus Magnuson (independently) Haruki Oyama (Waseda University, independently)
Show details on NVD website
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      "containers": "{\"adp\": [{\"title\": \"CISA ADP Vulnrichment\", \"metrics\": [{\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2026-34477\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"none\"}, {\"Automatable\": \"no\"}, {\"Technical Impact\": \"partial\"}], \"version\": \"2.0.3\", \"timestamp\": \"2026-04-10T17:36:46.652477Z\"}}}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2026-04-10T17:38:37.230Z\"}}], \"cna\": {\"title\": \"Apache Log4j Core: verifyHostName attribute silently ignored in TLS configuration, allowing hostname verification bypass\", \"source\": {\"discovery\": \"EXTERNAL\"}, \"credits\": [{\"lang\": \"en\", \"type\": \"finder\", \"value\": \"Samuli Leinonen (original reporter)\"}, {\"lang\": \"en\", \"type\": \"finder\", \"value\": \"Naresh Kandula (independently)\"}, {\"lang\": \"en\", \"type\": \"finder\", \"value\": \"Vitaly Simonovich (independently)\"}, {\"lang\": \"en\", \"type\": \"finder\", \"value\": \"Raijuna (independently)\"}, {\"lang\": \"en\", \"type\": \"finder\", \"value\": \"Danish Siddiqui (djvirus, independently)\"}, {\"lang\": \"en\", \"type\": \"finder\", \"value\": \"Markus Magnuson (independently)\"}, {\"lang\": \"en\", \"type\": \"finder\", \"value\": \"Haruki Oyama (Waseda University, independently)\"}], \"metrics\": [{\"format\": \"CVSS\", \"cvssV4_0\": {\"Safety\": \"NOT_DEFINED\", \"version\": \"4.0\", \"Recovery\": \"NOT_DEFINED\", \"baseScore\": 6.3, \"Automatable\": \"NOT_DEFINED\", \"attackVector\": \"NETWORK\", \"baseSeverity\": \"MEDIUM\", \"valueDensity\": \"NOT_DEFINED\", \"vectorString\": \"CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:L/SA:N\", \"providerUrgency\": \"NOT_DEFINED\", \"userInteraction\": \"NONE\", \"attackComplexity\": \"HIGH\", \"attackRequirements\": \"NONE\", \"privilegesRequired\": \"NONE\", \"subIntegrityImpact\": \"LOW\", \"vulnIntegrityImpact\": \"NONE\", \"subAvailabilityImpact\": \"NONE\", \"vulnAvailabilityImpact\": \"NONE\", \"subConfidentialityImpact\": \"NONE\", \"vulnConfidentialityImpact\": \"LOW\", \"vulnerabilityResponseEffort\": \"NOT_DEFINED\"}, \"scenarios\": [{\"lang\": \"en\", \"value\": \"GENERAL\"}]}, {\"other\": {\"type\": \"Textual description of severity\", \"content\": {\"text\": \"moderate\"}}}], \"affected\": [{\"cpes\": [\"cpe:2.3:a:apache:log4j:*:*:*:*:*:*:*:*\"], \"vendor\": \"Apache Software Foundation\", \"product\": \"Apache Log4j Core\", \"versions\": [{\"status\": \"affected\", \"version\": \"2.12.0\", \"lessThan\": \"2.25.4\", \"versionType\": \"maven\"}, {\"status\": \"affected\", \"version\": \"3.0.0-alpha1\", \"versionType\": \"maven\", \"lessThanOrEqual\": \"3.0.0-beta3\"}], \"packageURL\": \"pkg:maven/org.apache.logging.log4j/log4j-core\", \"packageName\": \"org.apache.logging.log4j:log4j-core\", \"collectionURL\": \"https://repo.maven.apache.org/maven2\", \"defaultStatus\": \"unaffected\"}], \"timeline\": [{\"lang\": \"en\", \"time\": \"2025-12-20T19:05:00.000Z\", \"value\": \"Vulnerability reported by Samuli Leinonen\"}, {\"lang\": \"en\", \"time\": \"2025-12-30T22:57:00.000Z\", \"value\": \"Candidate patch shared internally by Piotr P. Karwasz\"}, {\"lang\": \"en\", \"time\": \"2026-02-25T19:35:00.000Z\", \"value\": \"Independent report received from Naresh Kandula\"}, {\"lang\": \"en\", \"time\": \"2026-03-01T23:01:00.000Z\", \"value\": \"Independent report received from Vitaly Simonovich\"}, {\"lang\": \"en\", \"time\": \"2026-03-02T06:31:00.000Z\", \"value\": \"Independent report received from Raijuna\"}, {\"lang\": \"en\", \"time\": \"2026-03-08T18:17:00.000Z\", \"value\": \"Independent report received from Danish Siddiqui\"}, {\"lang\": \"en\", \"time\": \"2026-03-19T09:46:00.000Z\", \"value\": \"Independent report received from Markus Magnuson\"}, {\"lang\": \"en\", \"time\": \"2026-03-21T11:13:00.000Z\", \"value\": \"Independent report received from Haruki Oyama\"}, {\"lang\": \"en\", \"time\": \"2026-03-24T19:46:00.000Z\", \"value\": \"Fix shared publicly by Piotr P. Karwasz as pull request #4075\"}, {\"lang\": \"en\", \"time\": \"2026-03-28T11:19:00.000Z\", \"value\": \"Log4j 2.25.4 released\"}], \"references\": [{\"url\": \"https://github.com/apache/logging-log4j2/pull/4075\", \"tags\": [\"patch\"]}, {\"url\": \"https://logging.apache.org/security.html#CVE-2026-34477\", \"tags\": [\"vendor-advisory\"]}, {\"url\": \"https://logging.apache.org/cyclonedx/vdr.xml\", \"tags\": [\"vendor-advisory\"]}, {\"url\": \"https://logging.apache.org/log4j/2.x/manual/appenders/network.html#SslConfiguration-attr-verifyHostName\", \"tags\": [\"related\"]}, {\"url\": \"https://lists.apache.org/thread/lkx8cl46t2bvkcwfcb2pd43ygc097lq4\", \"tags\": [\"vendor-advisory\"]}], \"x_generator\": {\"engine\": \"Vulnogram 0.2.0\"}, \"descriptions\": [{\"lang\": \"en\", \"value\": \"The fix for  CVE-2025-68161 https://logging.apache.org/security.html#CVE-2025-68161  was incomplete: it addressed hostname verification only when enabled via the  log4j2.sslVerifyHostName https://logging.apache.org/log4j/2.x/manual/systemproperties.html#log4j2.sslVerifyHostName  system property, but not when configured through the  verifyHostName https://logging.apache.org/log4j/2.x/manual/appenders/network.html#SslConfiguration-attr-verifyHostName  attribute of the \u003cSsl\u003e element.\\n\\nAlthough the verifyHostName configuration attribute was introduced in Log4j Core 2.12.0, it was silently ignored in all versions through 2.25.3, leaving TLS connections vulnerable to interception regardless of the configured value.\\n\\nA network-based attacker may be able to perform a man-in-the-middle attack when all of the following conditions are met:\\n\\n  *  An SMTP, Socket, or Syslog appender is in use.\\n  *  TLS is configured via a nested \u003cSsl\u003e element.\\n  *  The attacker can present a certificate issued by a CA trusted by the appender\u0027s configured trust store, or by the default Java trust store if none is configured.\\nThis issue does not affect users of the HTTP appender, which uses a separate  verifyHostname https://logging.apache.org/log4j/2.x/manual/appenders/network.html#HttpAppender-attr-verifyHostName  attribute that was not subject to this bug and verifies host names by default.\\n\\nUsers are advised to upgrade to Apache Log4j Core 2.25.4, which corrects this issue.\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"\u003cp\u003eThe fix for \u003ca target=\\\"_blank\\\" rel=\\\"nofollow\\\" href=\\\"https://logging.apache.org/security.html#CVE-2025-68161\\\"\u003eCVE-2025-68161\u003c/a\u003e was incomplete: it addressed hostname verification only when enabled via the \u003ca target=\\\"_blank\\\" rel=\\\"nofollow\\\" href=\\\"https://logging.apache.org/log4j/2.x/manual/systemproperties.html#log4j2.sslVerifyHostName\\\"\u003e\u003ccode\u003elog4j2.sslVerifyHostName\u003c/code\u003e\u003c/a\u003e system property, but not when configured through the \u003ccode\u003e\u003ca target=\\\"_blank\\\" rel=\\\"nofollow\\\" href=\\\"https://logging.apache.org/log4j/2.x/manual/appenders/network.html#SslConfiguration-attr-verifyHostName\\\"\u003everifyHostName\u003c/a\u003e\u003c/code\u003e attribute of the \u003ccode\u003e\u0026lt;Ssl\u0026gt;\u003c/code\u003e element.\u003c/p\u003e\u003cp\u003eAlthough the \u003ccode\u003everifyHostName\u003c/code\u003e configuration attribute was introduced in Log4j Core 2.12.0, it was silently ignored in all versions through 2.25.3, leaving TLS connections vulnerable to interception regardless of the configured value.\u003c/p\u003e\u003cp\u003eA network-based attacker may be able to perform a man-in-the-middle attack when \u003cstrong\u003eall\u003c/strong\u003e of the following conditions are met:\u003c/p\u003e\u003col\u003e\u003cli\u003eAn SMTP, Socket, or Syslog appender is in use.\u003c/li\u003e\u003cli\u003eTLS is configured via a nested \u003ccode\u003e\u0026lt;Ssl\u0026gt;\u003c/code\u003e element.\u003c/li\u003e\u003cli\u003eThe attacker can present a certificate issued by a CA trusted by the appender\u0027s configured trust store, or by the default Java trust store if none is configured.\u003c/li\u003e\u003c/ol\u003e\u003cp\u003eThis issue does not affect users of the HTTP appender, which uses a separate \u003ccode\u003e\u003ca target=\\\"_blank\\\" rel=\\\"nofollow\\\" href=\\\"https://logging.apache.org/log4j/2.x/manual/appenders/network.html#HttpAppender-attr-verifyHostName\\\"\u003everifyHostname\u003c/a\u003e\u003c/code\u003e attribute that was not subject to this bug and verifies host names by default.\u003c/p\u003e\u003cp\u003eUsers are advised to upgrade to Apache Log4j Core 2.25.4, which corrects this issue.\u003c/p\u003e\", \"base64\": false}]}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-297\", \"description\": \"CWE-297 Improper Validation of Certificate with Host Mismatch\"}]}], \"providerMetadata\": {\"orgId\": \"f0158376-9dc2-43b6-827c-5f631a4d8d09\", \"shortName\": \"apache\", \"dateUpdated\": \"2026-04-10T15:36:19.740Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2026-34477\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-04-10T17:38:57.154Z\", \"dateReserved\": \"2026-03-28T11:26:04.052Z\", \"assignerOrgId\": \"f0158376-9dc2-43b6-827c-5f631a4d8d09\", \"datePublished\": \"2026-04-10T15:36:19.740Z\", \"assignerShortName\": \"apache\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}


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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.