MediumCVE-2021-45105

    Apache Log4j2 does not always protect from infinite recursion in lookup evaluation (CVE-2021-45105)

    Published Last modified Sources: SingCERT, Debian, OSV, Siemens ProductCERT, CVE.org, BSI

    What is affected, what to do

    Apache Log4j2 versions 2.0-alpha1 through 2.16.0 (excluding 2.12.3 and 2.3.1) did not protect from uncontrolled recursion from self-referential lookups. This allows an attacker with control over Thread Context Map data to cause a denial of service when a crafted string is interpreted.

    The vulnerability is being actively exploited; treat it as a priority. Update Apache Log4j2 to version 2.17.0.

    Affected
    • Apache Log4j2 lt log4j-core..2.17.0
    Fixed in
    • Apache Log4j2 2.17.0

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    5.9

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: NVD, CVSS v3

    5.9

    CVSS v3

    Severity Medium on the scale from 0 to 10.

    Source: SingCERT, Debian, OSV, Siemens ProductCERT, CVE.org, BSI

    —

    EPSS score

    No value is available for this vulnerability.

    Show all metrics
    Severity
    Medium
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    109.69 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    actively exploitedSource: ANSSI / CERT-FR How we classify
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    5.9 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    5.9
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    99.99
    Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    —
    Published
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-20, CWE-674

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    Apache Log4j2 versions 2.0-alpha1 through 2.16.0 (excluding 2.12.3 and 2.3.1) did not protect from uncontrolled recursion from self-referential lookups. This allows an attacker with control over Thread Context Map data to cause a denial of service when a crafted string is interpreted. This issue was fixed in Log4j 2.17.0, 2.12.3, and 2.3.1.

    Source: CSA/SingCERT, Debian Security Advisories, OSV (Open Source Vulnerabilities), siemens_advisory, cvelistv5, NVD (NIST), BSI CSAF, BSI WID Portal

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    Apache Software FoundationApache Log4j2
    • log4j-core – < 2.17.0
    • 2.17.0
    apachelog4j
    • 2.4 – < 2.12.3
    • 2.13.0 – ≤ 2.16.0
    • 2.0 – < 2.3.1
    • 2.12.3
    • —
    • 2.3.1
    netappcloud_manager
    • —
    • —
    oracleagile_engineering_data_management
    • 6.2.1.0
    • —
    oracleagile_plm_mcad_connector
    • 3.6
    • —
    oracleagile_product_lifecycle_management
    • 9.3.6
    • —
    oracleautovue_for_agile_product_lifecycle_management
    • 21.0.2
    • —
    oraclebanking_deposits_and_lines_of_credit_servicing
    • 2.12.0
    • —
    oraclebanking_enterprise_default_management
    • 2.12.0
    • 2.7.1
    • —
    • —
    oraclebanking_loans_servicing
    • 2.12.0
    • —
    oraclebanking_party_management
    • 2.7.0
    • —
    oraclebanking_payments
    • 14.5
    • —
    oraclebanking_platform
    • 2.6.2
    • 2.7.1
    • 2.12.0
    • —
    • —
    • —
    oraclebanking_trade_finance
    • 14.5
    • —
    oraclebanking_treasury_management
    • 14.5
    • —
    oraclebusiness_intelligence
    • 5.5.0.0.0
    • —
    oraclecommunications_asap
    • 7.3
    • —
    oraclecommunications_billing_and_revenue_management
    • 12.0.0.5
    • 12.0.0.4
    • —
    • —
    oraclecommunications_cloud_native_core_console
    • 1.9.0
    • —
    oraclecommunications_cloud_native_core_network_function_cloud_native_environment
    • 1.10.0
    • —
    oraclecommunications_cloud_native_core_network_repository_function
    • 1.15.0
    • 1.15.1
    • —
    • —
    oraclecommunications_cloud_native_core_network_slice_selection_function
    • 1.8.0
    • —
    oraclecommunications_cloud_native_core_policy
    • 1.15.0
    • —
    oraclecommunications_cloud_native_core_security_edge_protection_proxy
    • 1.7.0
    • —
    oraclecommunications_cloud_native_core_service_communication_proxy
    • 1.15.0
    • —
    oraclecommunications_cloud_native_core_unified_data_repository
    • 1.15.0
    • —
    oraclecommunications_convergence
    • 3.0.2.2.0
    • 3.0.3.0
    • —
    • —
    oraclecommunications_convergent_charging_controller
    • 12.0.1.0.0 – ≤ 12.0.4.0.0
    • 6.0.1.0.0
    • —
    • —
    oraclecommunications_diameter_signaling_router
    • 8.3.0.0 – ≤ 8.5.1.0
    • —
    oraclecommunications_eagle_element_management_system
    • 46.6
    • —
    oraclecommunications_eagle_ftp_table_base_retrieval
    • 4.5
    • —
    oraclecommunications_element_manager
    • < 9.0
    • 9.0
    oraclecommunications_evolved_communications_application_server
    • 7.1
    • —
    oraclecommunications_interactive_session_recorder
    • 6.3
    • 6.4
    • —
    • —
    oraclecommunications_ip_service_activator
    • 7.4.0
    • —
    oraclecommunications_messaging_server
    • 8.1
    • —
    oraclecommunications_network_charging_and_control
    • 12.0.1.0.0 – ≤ 12.0.4.0.0
    • 6.0.1.0.0
    • —
    • —

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxdebianapache-log4j2bullseye
    Linuxdebianapache-log4j2buster
    Linuxdebiandebian_linux10.0
    Linuxdebiandebian_linux11.0
    Othersonicwall6bk1602-0aa12-0tp0_firmware—
    Othersonicwall6bk1602-0aa22-0tp0_firmware—
    Othersonicwall6bk1602-0aa32-0tp0_firmware—
    Othersonicwall6bk1602-0aa42-0tp0_firmware—
    Othersonicwall6bk1602-0aa52-0tp0_firmware—

    Weakness classes (CWE)

    • CWE-20Improper Input Validation

      Class

      The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.

      Entry at MITRE CWE-20

    • CWE-674Uncontrolled Recursion

      Class

      The product does not properly control the amount of recursion that takes place, consuming excessive resources, such as allocated memory or the program stack.

      Entry at MITRE CWE-674

    Public exploit references

    Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

    Public exploit references
    ANSSI / CERT-FRLicence Ouverte 2.0, as of CERTFR-2021-ALE-022 – [MaJ] Vulnérabilité dans Apache Log4j (clôturée 2022-05-04) (opens in a new tab)cert.cyber.gouv.fractively exploited

    References & sources

    Changes to this CVE

    Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

    1. Product identifiers remappedNVD

      Product mapping changed:
      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Product configurationchanged
      OR *cpe:2.3:a:oracle:agile_plm:9.3.6:*:*:*:*:*:*:*
      OR *cpe:2.3:a:oracle:agile_product_lifecycle_management:9.3.6:*:*:*:*:*:*:*

      Source identifier: nvd@nist.gov

    Linked advisories

    Embed badge

    Show the severity and KEV status of this vulnerability on your site – with a link back here. The image is updated hourly.

    Badge preview for CVE-2021-45105
    <a href="https://intel.neosec.eu/en/cve/CVE-2021-45105"><img src="https://intel.neosec.eu/badge/cve/CVE-2021-45105.svg?lang=en" alt="CVE-2021-45105 – NEOSEC Intel" height="20"></a>