CriticalCVE-2009-0557

    Microsoft Office Object Record Corruption Vulnerability (CVE-2009-0557)

    Published In CISA KEV since Sources: CVE.org

    What is affected, what to do

    Excel in Microsoft Office 2000 SP3, Office XP SP3, Office 2003 SP3, and Office 2004 and 2008 for Mac; Excel in 2007 Microsoft Office System SP1 and SP2; Open XML File Format Converter for Mac; Microsoft Office Excel Viewer 2003 SP3; Microsoft Office Excel Viewer; and Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats SP1 and SP2 allow remote attackers to execute arbitrary code via a crafted Excel file with a malformed record object, aka "Object Record Corruption Vulnerability."

    The vulnerability is being actively exploited; treat it as a priority. The available sources name no fixed version. Check the vendor guidance in the references below. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Microsoft Office eq 2000..2000
    • Microsoft Office eq 2003..2003
    • Microsoft Office eq 2004..2004
    • Microsoft Office eq 2007..2007
    • Microsoft Office eq 2008..2008
    • Microsoft Office eq xp..xp
    • Microsoft Office Compatibility Pack Service Pack 3 eq 2007..2007
    • Microsoft Office Excel Viewer eq 2003..2003
    • Microsoft Office Sharepoint Server eq 2007..2007

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

    Metrics

    7.8

    Priority

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

    Source: NVD, CVSS v3

    7.8

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: CVE.org

    52.8 %

    EPSS score

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

    Source: FIRST EPSS, percentile 99.0

    Show all metrics
    Severity
    Critical
    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
    217.36 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 exploited
    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
    7.8 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
    7.8
    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
    52.8 %
    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
    Actively exploited
    Published
    In CISA KEV since

    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

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This CVE sits on KEV because weaponised Excel files have long been used as spear-phishing attachments for initial code execution: the attack needs only a user to open the file, no authentication, and success means full compromise of confidentiality, integrity and availability in the user's context. Exploitation likelihood is rated very high, while CISA has not flagged ransomware use. Typical targets are organisations with long-lived legacy estates — business units clinging to old macros, terminal servers, engineering and OT-adjacent workstations. If your inventory comes back clean, the residual risk is negligible; if it returns hits, treat this as high priority, because end-of-life Office leaves you exposed to many further unpatched flaws — a finding that NIS2 asset and vulnerability management will expect you to close.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Inventory legacy installs: Use SCCM/Intune or Defender TVM to find every endpoint running Office 2000, XP, 2003, 2007, Office 2004/2008 for Mac, Excel Viewer (2003 and later) or the Office Compatibility Pack 2007. Example KQL: DeviceTvmSoftwareInventory | where SoftwareName has_any ("office","excel_viewer","compatibility_pack") and toint(split(SoftwareVersion,".")[0]) <= 12
      • Patch vs. retire: A vendor security update exists (to our knowledge Security Bulletin MS09-021, June 2009 — verify in the vendor advisory). Every affected product is end-of-life and receives no further fixes, so the real goal is uninstalling or migrating to a supported Microsoft 365 Apps / Office LTSC build, not just back-patching.
      • Remove Excel Viewer and the Compatibility Pack: These frequently linger on clients and terminal servers alongside newer Office builds and register themselves as .xls handlers. Uninstall them first.
      • Isolate systems that cannot be migrated: Line-of-business, OT or engineering workstations that genuinely require Office 2003/2007 go into a dedicated segment with no mail or internet access; file intake only via a controlled transfer point.
      • Tighten the mail gateway now: Quarantine or sandbox-detonate inbound BIFF-format Excel binaries (.xls, .xlt, .xla) from external senders.

    2. Runbook step 2

      Mitigation layers

      • Configuration (File Block): Via Group Policy, set Trust Center File Block settings for Excel 97-2003 binary and older formats to "Do not open" or "Open in Protected View". For legacy Office 2003/2007, the vendor's workaround at the time was MOICE (Microsoft Office Isolated Conversion Environment) — use only as a stopgap.
      • Endpoint hardening (ASR): Enable the ASR rules "Block all Office applications from creating child processes" (D4F940AB-401B-4EFC-AADC-AD5F3C50688A) and "Block Office applications from creating executable content" (3B576869-A4EC-4529-8536-B80A7769E899) in block mode. Back them up with AppLocker/WDAC rules preventing execution from %TEMP% and %APPDATA% on hosts running unsupported Office.
      • Exploit protection: Force DEP and ASLR (Mandatory ASLR, Bottom-up ASLR) for EXCEL.EXE through Windows Defender Exploit Protection. Old Office binaries were not built ASLR-aware; system-level enforcement makes memory-corruption exploits considerably harder.
      • IAM / least privilege: Users on legacy-Office hosts must not hold local admin rights, so user-context code execution cannot easily gain system-level persistence.
      • Network / content inspection: Block .xls downloads from uncategorised or newly registered domains at the proxy and mail gateway. Enable IDS signatures for malformed BIFF object (OBJ) records in your Suricata/Snort rulesets and apply them to SMTP and HTTP.

    3. Runbook step 3

      Detection rules

      • Process ancestry (Sysmon EID 1 / MDE DeviceProcessEvents): EXCEL.EXE spawning cmd.exe, powershell.exe, wscript.exe, cscript.exe, mshta.exe, rundll32.exe or regsvr32.exe. Sigma shape: ParentImage|endswith: '\EXCEL.EXE' plus Image|endswith over that list.
      • Crash events: Windows Application log Event ID 1000/1001 with Faulting application name: EXCEL.EXE on legacy builds — failed exploitation attempts often crash the process. Escalate clusters that follow the opening of a mail attachment.
      • File creation (Sysmon EID 11): EXCEL.EXE writing .exe, .dll, .scr or .vbs into user or temp directories. KQL: DeviceFileEvents | where InitiatingProcessFileName =~ "excel.exe" and (FileName endswith ".exe" or FileName endswith ".dll")
      • Network telemetry (Sysmon EID 3 / Zeek conn.log): Outbound connections initiated directly by EXCEL.EXE to external IPs, especially on unusual ports or without a preceding DNS lookup.
      • Attachment analysis: Run inbound .xls attachments through oletools (oledump.py, olevba) or a sandbox; treat structurally malformed BIFF records or embedded shellcode as an indicator.

    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

    Excel in Microsoft Office 2000 SP3, Office XP SP3, Office 2003 SP3, and Office 2004 and 2008 for Mac; Excel in 2007 Microsoft Office System SP1 and SP2; Open XML File Format Converter for Mac; Microsoft Office Excel Viewer 2003 SP3; Microsoft Office Excel Viewer; and Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats SP1 and SP2 allow remote attackers to execute arbitrary code via a crafted Excel file with a malformed record object, aka "Object Record Corruption Vulnerability."

    Source: NVD (NIST), cvelistv5, CISA KEV Catalog, CVE.org (MITRE)

    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
    microsoftoffice
    • 2000
    • xp
    • 2003
    • 2007
    • 2008
    • 2004
    • —
    • —
    • —
    • —
    • —
    • —
    microsoftoffice_compatibility_pack
    • 2007
    • —
    microsoftoffice_excel_viewer
    • 2003
    • —
    • —
    • —
    microsoftoffice_sharepoint_server
    • 2007
    • —
    microsoftopen_xml_file_format_converter
    • —
    • —

    Vendors and products

    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
    CISA KEV CatalogCISA Known Exploited Vulnerability (opens in a new tab)cisa.govactively exploited

    References & sources

    • vupen.comADV-2009-1540Vulnerability database, x_refsource_VUPEN, Broken link
    • oval.cisecurity.orgoval:org.mitre.oval:def:5564Vulnerability database, signature, x_refsource_OVAL, Broken link
    • securitytracker.com1022351Vulnerability database, x_refsource_SECTRACK, Broken link, Third-party advisory, Vulnerability database
    • docs.microsoft.comMS09-021Vendor advisory, x_refsource_MS, Patch, Vendor advisory
    • osvdb.org54953Vulnerability database, x_refsource_OSVDB, Broken link
    • securityfocus.com35241Vulnerability database, x_refsource_BID, Broken link, Third-party advisory, Vulnerability database
    • us-cert.govTA09-160AThird-party advisory, x_refsource_CERT, Broken link, Third-party advisory, US government resource
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2009-0557government-resource, US government resource
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