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
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-04-10 17:36 UTC
CWE
  • CWE-297 - Improper Validation of Certificate with Host Mismatch
Assigner
References
Impacted products
Vendor Product Version CPE status
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
To clipboard 

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            "tags": [
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          },
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            "tags": [
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        "vulnStatus": "Analyzed",
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                "value": "CWE-297"
              }
            ],
            "source": "security@apache.org",
            "type": "Secondary"
          },
          {
            "description": [
              {
                "lang": "en",
                "value": "CWE-295"
              }
            ],
            "source": "nvd@nist.gov",
            "type": "Primary"
          }
        ]
      }
    },
    "redhat_vex": {
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      "current_release_date": "2026-09-21T17:13:50+00:00",
      "cve": "CVE-2026-34477",
      "id": "CVE-2026-34477",
      "initial_release_date": "2026-04-10T15:36:19.740000+00:00",
      "product_status:fixed": "2",
      "product_status:known_affected": "59",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "org.apache.logging.log4j/log4j-core: Apache Log4j Core: Man-in-the-middle attack due to incomplete hostname verification",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-34477.json",
      "version": "3"
    },
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      "current_release_date": "2026-06-26T02:20:38Z",
      "cve": "CVE-2026-34477",
      "id": "CVE-2026-34477",
      "initial_release_date": "2026-04-14T23:26:08Z",
      "product_status:known_affected": "56",
      "product_status:known_not_affected": "10",
      "product_status:recommended": "33",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-34477",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-34477.json",
      "version": "4"
    },
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                    "role": "CISA Coordinator",
                    "timestamp": "2026-04-10T17:36:46.652477Z",
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              "type": "finder",
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            },
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            },
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                "valueDensity": "NOT_DEFINED",
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                "vulnAvailabilityImpact": "NONE",
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                "vulnIntegrityImpact": "NONE",
                "vulnerabilityResponseEffort": "NOT_DEFINED"
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              "format": "CVSS",
              "scenarios": [
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                  "lang": "en",
                  "value": "GENERAL"
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            },
            {
              "other": {
                "content": {
                  "text": "moderate"
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                "type": "Textual description of severity"
              }
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          ],
          "problemTypes": [
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              "descriptions": [
                {
                  "cweId": "CWE-297",
                  "description": "CWE-297 Improper Validation of Certificate with Host Mismatch",
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                  "type": "CWE"
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              "time": "2025-12-30T22:57:00.000Z",
              "value": "Candidate patch shared internally by Piotr P. Karwasz"
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              "lang": "en",
              "time": "2026-02-25T19:35:00.000Z",
              "value": "Independent report received from Naresh Kandula"
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              "value": "Independent report received from Vitaly Simonovich"
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              "lang": "en",
              "time": "2026-03-02T06:31:00.000Z",
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              "value": "Independent report received from Danish Siddiqui"
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              "time": "2026-03-24T19:46:00.000Z",
              "value": "Fix shared publicly by Piotr P. Karwasz as pull request #4075"
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              "time": "2026-03-28T11:19:00.000Z",
              "value": "Log4j 2.25.4 released"
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}



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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

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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.



Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.