HighCVE-2018-20843

    libexpat Project libexpat: Denial of Service (CVE-2018-20843)

    Published Last modified Sources: CVE.org, Red Hat

    What is affected, what to do

    In libexpat in Expat before 2.2.7, XML input including XML names that contain a large number of colons could make the XML parser consume a high amount of RAM and CPU resources while processing (enough to be usable for denial-of-service attacks).

    Update libexpat Project libexpat to version 2.2.7, Tenable Nessus to version 8.15.0.

    Affected
    • libexpat Project libexpat lt *..2.2.7
    • Canonical Ubuntu Linux eq 12.04..12.04
    • Canonical Ubuntu Linux eq 14.04..14.04
    • Canonical Ubuntu Linux eq 16.04..16.04
    • Canonical Ubuntu Linux eq 18.04..18.04
    • Canonical Ubuntu Linux eq 18.10..18.10
    • Canonical Ubuntu Linux eq 19.04..19.04
    • Debian Linux eq 8.0..8.0
    • Debian Linux eq 9.0..9.0
    • Fedora eq 29..29
    • Fedora eq 30..30
    • openSUSE Leap eq 15.0..15.0
    • openSUSE Leap eq 15.1..15.1
    • Oracle Hospitality RES 3700 lte 5.7..5.7.6
    • Oracle HTTP Server eq 12.1.3.0..12.1.3.0
    • Oracle HTTP Server eq 12.2.1.4.0..12.2.1.4.0
    • Oracle Outside In Technology eq 8.5.4..8.5.4
    • Oracle Outside In Technology eq 8.5.5..8.5.5
    • Tenable Nessus lt *..8.15.0
    Fixed in
    • libexpat Project libexpat 2.2.7
    • Tenable Nessus 8.15.0

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

    Metrics

    7.5

    Priority

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

    Source: NVD, CVSS v3

    7.5

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: CVE.org, Red Hat

    7.1 %

    EPSS score

    Moderate — model estimates 1-10% exploitation likelihood.

    Source: FIRST EPSS, percentile 94.2

    Show all metrics
    Severity
    High
    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
    108.52 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
    no public PoC known
    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
    7.5 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
    7.5
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    7.1 %
    Moderate — model estimates 1-10% exploitation likelihood.
    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
    94.2
    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
    CISA assessment (SSVC)
    Exploitation: none known · automatable · Technical impact: partial
    Source: CISA Vulnrichment, as of 30 May 2025
    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-611

    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
    High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
    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
    From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
    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

    In libexpat in Expat before 2.2.7, XML input including XML names that contain a large number of colons could make the XML parser consume a high amount of RAM and CPU resources while processing (enough to be usable for denial-of-service attacks).

    Source: cvelistv5, NVD (NIST), redhat_csaf

    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
    libexpat_projectlibexpat
    • < 2.2.7
    • 2.2.7
    oraclehospitality_res_3700
    • 5.7 – ≤ 5.7.6
    • —
    oraclehttp_server
    • 12.2.1.4.0
    • 12.1.3.0
    • —
    • —
    oracleoutside_in_technology
    • 8.5.4
    • 8.5.5
    • —
    • —
    tenablenessus
    • < 8.15.0
    • 8.15.0

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxdebiandebian_linux8.0
    Linuxdebiandebian_linux9.0
    Linuxopensuseleap15.0
    Linuxopensuseleap15.1
    Linuxcanonicalubuntu_linux12.04
    Linuxcanonicalubuntu_linux14.04
    Linuxcanonicalubuntu_linux16.04
    Linuxcanonicalubuntu_linux18.04
    Linuxcanonicalubuntu_linux18.10
    Linuxcanonicalubuntu_linux19.04
    Otherfedoraprojectfedora29
    Otherfedoraprojectfedora30

    Weakness classes (CWE)

    • CWE-611Improper Restriction of XML External Entity Reference

      Base

      The product processes an XML document that can contain XML entities with URIs that resolve to documents outside of the intended sphere of control, causing the product to embed incorrect documents into its output.

      Entry at MITRE CWE-611

    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. Record modifiedMITRE

      Show 61 original changes
      Individual changes of this event as published by NVD
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      Referenceadded
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      http://lists.opensuse.org/opensuse-security-announce/2019-07/msg00039.html
      Referenceadded
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      https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=5226
      Referenceadded
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      https://github.com/libexpat/libexpat/blob/R_2_2_7/expat/Changes
      Referenceadded
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      https://github.com/libexpat/libexpat/issues/186
      Referenceadded
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      https://github.com/libexpat/libexpat/pull/262
      Referenceadded
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      https://github.com/libexpat/libexpat/pull/262/commits/11f8838bf99ea0a6f0b76f9760c43704d00c4ff6
      Referenceadded
      —
      https://lists.debian.org/debian-lts-announce/2019/06/msg00028.html
      Referenceadded
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      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/CEJJSQSG3KSUQY4FPVHZ7ZTT7FORMFVD/
      Referenceadded
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      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/IDAUGEB3TUP6NEKJDBUBZX7N5OAUOOOK/
      Referenceadded
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      https://seclists.org/bugtraq/2019/Jun/39
      Referenceadded
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      https://security.gentoo.org/glsa/201911-08
      Referenceadded
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      https://security.netapp.com/advisory/ntap-20190703-0001/
      Referenceadded
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      https://support.f5.com/csp/article/K51011533
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      https://usn.ubuntu.com/4040-1/
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      https://usn.ubuntu.com/4040-2/
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      https://www.debian.org/security/2019/dsa-4472
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      https://www.oracle.com/security-alerts/cpuapr2020.html
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      https://www.oracle.com/security-alerts/cpuApr2021.html
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      https://www.oracle.com/security-alerts/cpuoct2020.html
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      https://www.oracle.com/security-alerts/cpuoct2021.html
      Referenceadded
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      https://www.tenable.com/security/tns-2021-11
      Referenceremoved
      http://lists.opensuse.org/opensuse-security-announce/2019-07/msg00039.html
      —
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      https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=5226
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      https://github.com/libexpat/libexpat/blob/R_2_2_7/expat/Changes
      —
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      https://github.com/libexpat/libexpat/issues/186
      —
      Referenceremoved
      https://github.com/libexpat/libexpat/pull/262
      —
      Referenceremoved
      https://github.com/libexpat/libexpat/pull/262/commits/11f8838bf99ea0a6f0b76f9760c43704d00c4ff6
      —
      Referenceremoved
      https://lists.debian.org/debian-lts-announce/2019/06/msg00028.html
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      Referenceremoved
      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/CEJJSQSG3KSUQY4FPVHZ7ZTT7FORMFVD/
      —
      Referenceremoved
      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/IDAUGEB3TUP6NEKJDBUBZX7N5OAUOOOK/
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      https://seclists.org/bugtraq/2019/Jun/39
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      https://security.gentoo.org/glsa/201911-08
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      https://security.netapp.com/advisory/ntap-20190703-0001/
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      https://support.f5.com/csp/article/K51011533
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      https://usn.ubuntu.com/4040-1/
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      https://usn.ubuntu.com/4040-2/
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      https://www.debian.org/security/2019/dsa-4472
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      https://www.oracle.com/security-alerts/cpuapr2020.html
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      https://www.oracle.com/security-alerts/cpuApr2021.html
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      https://www.oracle.com/security-alerts/cpuoct2020.html
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      https://www.oracle.com/security-alerts/cpuoct2021.html
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      Referenceremoved
      https://www.tenable.com/security/tns-2021-11
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      Reference typeremoved
      http://lists.opensuse.org/opensuse-security-announce/2019-07/msg00039.html Types: Mailing List, Third Party Advisory
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      Reference typeremoved
      https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=5226 Types: Issue Tracking, Third Party Advisory
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      Reference typeremoved
      https://github.com/libexpat/libexpat/blob/R_2_2_7/expat/Changes Types: Release Notes, Third Party Advisory
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      Reference typeremoved
      https://github.com/libexpat/libexpat/issues/186 Types: Issue Tracking, Patch, Third Party Advisory
      —
      Reference typeremoved
      https://github.com/libexpat/libexpat/pull/262 Types: Exploit, Patch, Third Party Advisory
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      Reference typeremoved
      https://github.com/libexpat/libexpat/pull/262/commits/11f8838bf99ea0a6f0b76f9760c43704d00c4ff6 Types: Patch, Third Party Advisory
      —
      Reference typeremoved
      https://lists.debian.org/debian-lts-announce/2019/06/msg00028.html Types: Mailing List, Third Party Advisory
      —
      Reference typeremoved
      https://seclists.org/bugtraq/2019/Jun/39 Types: Mailing List, Third Party Advisory
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      Reference typeremoved
      https://security.gentoo.org/glsa/201911-08 Types: Third Party Advisory
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      Reference typeremoved
      https://security.netapp.com/advisory/ntap-20190703-0001/ Types: Third Party Advisory
      —
      Reference typeremoved
      https://support.f5.com/csp/article/K51011533 Types: Third Party Advisory
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      https://usn.ubuntu.com/4040-1/ Types: Third Party Advisory
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      Reference typeremoved
      https://usn.ubuntu.com/4040-2/ Types: Third Party Advisory
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      Reference typeremoved
      https://www.debian.org/security/2019/dsa-4472 Types: Third Party Advisory
      —
      Reference typeremoved
      https://www.oracle.com/security-alerts/cpuapr2020.html Types: Patch, Third Party Advisory
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      Reference typeremoved
      https://www.oracle.com/security-alerts/cpuApr2021.html Types: Patch, Third Party Advisory
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      Reference typeremoved
      https://www.oracle.com/security-alerts/cpuoct2020.html Types: Patch, Third Party Advisory
      —
      Reference typeremoved
      https://www.oracle.com/security-alerts/cpuoct2021.html Types: Patch, Third Party Advisory
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      Reference typeremoved
      https://www.tenable.com/security/tns-2021-11 Types: Third Party Advisory
      —

      Source identifier: cve@mitre.org

    2. Record modifiedCVE Program

      Show 61 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
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      http://lists.opensuse.org/opensuse-security-announce/2019-07/msg00039.html
      Referenceadded
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      https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=5226
      Referenceadded
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      https://github.com/libexpat/libexpat/blob/R_2_2_7/expat/Changes
      Referenceadded
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      https://github.com/libexpat/libexpat/issues/186
      Referenceadded
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      https://github.com/libexpat/libexpat/pull/262
      Referenceadded
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      https://github.com/libexpat/libexpat/pull/262/commits/11f8838bf99ea0a6f0b76f9760c43704d00c4ff6
      Referenceadded
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      https://lists.debian.org/debian-lts-announce/2019/06/msg00028.html
      Referenceadded
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      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/CEJJSQSG3KSUQY4FPVHZ7ZTT7FORMFVD/
      Referenceadded
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      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/IDAUGEB3TUP6NEKJDBUBZX7N5OAUOOOK/
      Referenceadded
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      https://seclists.org/bugtraq/2019/Jun/39
      Referenceadded
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      https://security.gentoo.org/glsa/201911-08
      Referenceadded
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      https://security.netapp.com/advisory/ntap-20190703-0001/
      Referenceadded
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      https://support.f5.com/csp/article/K51011533
      Referenceadded
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      https://usn.ubuntu.com/4040-1/
      Referenceadded
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      https://usn.ubuntu.com/4040-2/
      Referenceadded
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      https://www.debian.org/security/2019/dsa-4472
      Referenceadded
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      https://www.oracle.com/security-alerts/cpuapr2020.html
      Referenceadded
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      https://www.oracle.com/security-alerts/cpuApr2021.html
      Referenceadded
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      https://www.oracle.com/security-alerts/cpuoct2020.html
      Referenceadded
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      https://www.oracle.com/security-alerts/cpuoct2021.html
      Referenceadded
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      https://www.tenable.com/security/tns-2021-11
      Referenceremoved
      http://lists.opensuse.org/opensuse-security-announce/2019-07/msg00039.html
      —
      Referenceremoved
      https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=5226
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      https://github.com/libexpat/libexpat/blob/R_2_2_7/expat/Changes
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      https://github.com/libexpat/libexpat/issues/186
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      https://github.com/libexpat/libexpat/pull/262
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      https://github.com/libexpat/libexpat/pull/262/commits/11f8838bf99ea0a6f0b76f9760c43704d00c4ff6
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      Referenceremoved
      https://lists.debian.org/debian-lts-announce/2019/06/msg00028.html
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      Referenceremoved
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      https://seclists.org/bugtraq/2019/Jun/39
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      https://security.gentoo.org/glsa/201911-08
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      https://security.netapp.com/advisory/ntap-20190703-0001/
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      https://support.f5.com/csp/article/K51011533
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      https://usn.ubuntu.com/4040-1/
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      https://www.debian.org/security/2019/dsa-4472
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      https://www.oracle.com/security-alerts/cpuapr2020.html
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      https://www.oracle.com/security-alerts/cpuApr2021.html
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      https://www.oracle.com/security-alerts/cpuoct2021.html
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      Referenceremoved
      https://www.tenable.com/security/tns-2021-11
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      Reference typeremoved
      http://lists.opensuse.org/opensuse-security-announce/2019-07/msg00039.html Types: Mailing List, Third Party Advisory
      —
      Reference typeremoved
      https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=5226 Types: Issue Tracking, Third Party Advisory
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      Reference typeremoved
      https://github.com/libexpat/libexpat/blob/R_2_2_7/expat/Changes Types: Release Notes, Third Party Advisory
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      Reference typeremoved
      https://github.com/libexpat/libexpat/issues/186 Types: Issue Tracking, Patch, Third Party Advisory
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      Reference typeremoved
      https://github.com/libexpat/libexpat/pull/262 Types: Exploit, Patch, Third Party Advisory
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      Reference typeremoved
      https://github.com/libexpat/libexpat/pull/262/commits/11f8838bf99ea0a6f0b76f9760c43704d00c4ff6 Types: Patch, Third Party Advisory
      —
      Reference typeremoved
      https://lists.debian.org/debian-lts-announce/2019/06/msg00028.html Types: Mailing List, Third Party Advisory
      —
      Reference typeremoved
      https://seclists.org/bugtraq/2019/Jun/39 Types: Mailing List, Third Party Advisory
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      Reference typeremoved
      https://security.gentoo.org/glsa/201911-08 Types: Third Party Advisory
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      Reference typeremoved
      https://security.netapp.com/advisory/ntap-20190703-0001/ Types: Third Party Advisory
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      Reference typeremoved
      https://support.f5.com/csp/article/K51011533 Types: Third Party Advisory
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      Reference typeremoved
      https://usn.ubuntu.com/4040-1/ Types: Third Party Advisory
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      Reference typeremoved
      https://usn.ubuntu.com/4040-2/ Types: Third Party Advisory
      —
      Reference typeremoved
      https://www.debian.org/security/2019/dsa-4472 Types: Third Party Advisory
      —
      Reference typeremoved
      https://www.oracle.com/security-alerts/cpuapr2020.html Types: Patch, Third Party Advisory
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      Reference typeremoved
      https://www.oracle.com/security-alerts/cpuApr2021.html Types: Patch, Third Party Advisory
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      Reference typeremoved
      https://www.oracle.com/security-alerts/cpuoct2020.html Types: Patch, Third Party Advisory
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      Reference typeremoved
      https://www.oracle.com/security-alerts/cpuoct2021.html Types: Patch, Third Party Advisory
      —
      Reference typeremoved
      https://www.tenable.com/security/tns-2021-11 Types: Third Party Advisory
      —

      Source identifier: af854a3a-2127-422b-91ae-364da2661108

    3. Record modifiedSiemens ADP

      Show 2 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Affected versions (publisher)added
      —
      New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2018/20xxx/CVE-2018-20843.json">CVE-2018-20843</a>
      Referenceadded
      —
      https://cert-portal.siemens.com/productcert/html/ssa-398330.html

      Source identifier: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e

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