HighCVE-2009-1955

    Apache Portable Runtime Utility: Denial of Service (CVE-2009-1955)

    Published Sources: CVE.org

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    What is affected, what to do

    The expat XML parser in the apr_xml_* interface in xml/apr_xml.c in Apache APR-util before 1.3.7, as used in the mod_dav and mod_dav_svn modules in the Apache HTTP Server, allows remote attackers to cause a denial of service (memory consumption) via a crafted XML document containing a large number of nested entity references, as demonstrated by a PROPFIND request, a similar issue to CVE-2003-1564.

    An exploit is publicly available. Update Apache Portable Runtime Utility to version 1.3.7, Apple Mac OS X to version 10.6.2, Apache HTTP Server to version 2.2.12.

    Affected
    • Apache Portable Runtime Utility lt *..1.3.7
    • Apple Mac OS X lt *..10.6.2
    • SUSE Linux Enterprise Server eq 9..9
    • Debian Linux eq 4.0..4.0
    • Canonical Ubuntu Linux eq 6.06..6.06
    • Canonical Ubuntu Linux eq 8.04..8.04
    • Canonical Ubuntu Linux eq 8.10..8.10
    • Canonical Ubuntu Linux eq 9.04..9.04
    • Fedora eq 9..9
    • Fedora eq 10..10
    • Fedora eq 11..11
    • Apache HTTP Server lt 2.2.0..2.2.12
    Fixed in
    • Apache Portable Runtime Utility 1.3.7
    • Apple Mac OS X 10.6.2
    • Apache HTTP Server 2.2.12

    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

    53.0 %

    EPSS score

    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.

    Source: FIRST EPSS, percentile 99.0

    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
    115.88 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
    PoC (publicly reported)
    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
    53.0 %
    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.
    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
    99.0
    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

    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

    The expat XML parser in the apr_xml_* interface in xml/apr_xml.c in Apache APR-util before 1.3.7, as used in the mod_dav and mod_dav_svn modules in the Apache HTTP Server, allows remote attackers to cause a denial of service (memory consumption) via a crafted XML document containing a large number of nested entity references, as demonstrated by a PROPFIND request, a similar issue to CVE-2003-1564.

    Source: NVD (NIST), cvelistv5

    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
    apacheapr-util
    • < 1.3.7
    • 1.3.7
    apachehttp_server
    • 2.2.0 – < 2.2.12
    • 2.2.12
    oraclehttp_server
    • —
    • —

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxdebiandebian_linux4.0
    Linuxsuselinux_enterprise_server9
    Linuxcanonicalubuntu_linux6.06
    Linuxcanonicalubuntu_linux8.04
    Linuxcanonicalubuntu_linux8.10
    Linuxcanonicalubuntu_linux9.04
    macOSapplemac_os_x—
    Otherfedoraprojectfedora10
    Otherfedoraprojectfedora11
    Otherfedoraprojectfedora9

    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
    Exploit-DBEDB-ID 8842 (opens in a new tab)exploit-db.comPoC (publicly reported)reported, not verified—

    References & sources

    • secunia.com35487Third-party advisory, x_refsource_SECUNIA, Broken link, Third-party advisory
    • debian.orgDSA-1812Vendor advisory, x_refsource_DEBIAN, Mailing list, Third-party advisory
    • apache.orgdist/apr/CHANGES-APR-UTIL-1.3x_refsource_CONFIRM, Broken link
    • vupen.comADV-2009-1907Vulnerability database, x_refsource_VUPEN, Broken link, Third-party advisory
    • redhat.comFEDORA-2009-5969Vendor advisory, x_refsource_FEDORA, Mailing list
    • secunia.com35444Third-party advisory, x_refsource_SECUNIA, Broken link, Third-party advisory
    • marc.info[apr-dev] 20090602 [PATCH] prevent "billion laughs" attack against expatMailing list, x_refsource_MLIST, Mailing list, Patch
    • mandriva.comMDVSA-2009:131Vendor advisory, x_refsource_MANDRIVA, Broken link, Third-party advisory
    • oval.cisecurity.orgoval:org.mitre.oval:def:10270Vulnerability database, signature, x_refsource_OVAL, Broken link, Third-party advisory
    • secunia.com35360Third-party advisory, x_refsource_SECUNIA, Broken link, Third-party advisory
    • vupen.comADV-2010-1107Vulnerability database, x_refsource_VUPEN, Broken link, Third-party advisory
    • openwall.com[oss-security] 20090603 CVE request: "billion laughs" attack against Apache APRMailing list, x_refsource_MLIST, Mailing list
    • secunia.com35395Third-party advisory, x_refsource_SECUNIA, Broken link, Third-party advisory
    • www-01.ibm.comPK99478Vendor advisory, x_refsource_AIXAPAR, Broken link, Third-party advisory
    • securityfocus.com20090824 rPSA-2009-0123-1 apr-utilMailing list, x_refsource_BUGTRAQ, Broken link, Third-party advisory, Vulnerability database
    • lists.opensuse.orgSUSE-SR:2010:011Vendor advisory, x_refsource_SUSE, Mailing list, Third-party advisory
    • secunia.com35284Third-party advisory, x_refsource_SECUNIA, Broken link, Third-party advisory
    • www-01.ibm.comPK91241Vendor advisory, x_refsource_AIXAPAR, Broken link, Third-party advisory
    • secunia.com36473Third-party advisory, x_refsource_SECUNIA, Broken link, Third-party advisory
    • www-01.ibm.comPK88342Vendor advisory, x_refsource_AIXAPAR, Broken link
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