CVE-2009-0556: Microsoft Office High-Severity Vulnerability

What is CVE-2009-0556?

Microsoft Office PowerPoint 2000 SP3, 2002 SP3, and 2003 SP3, and PowerPoint in Microsoft Office 2004 for Mac, allows remote attackers to execute arbitrary code via a PowerPoint file with an OutlineTextRefAtom containing an an invalid index value that triggers memory corruption, as exploited in the wild in April 2009 by Exploit:Win32/Apptom.gen, aka "Memory Corruption Vulnerability."

Technical Analysis

Weakness Classification

This vulnerability is classified as CWE-94 — Code Injection. The application allows user input to be interpreted as code, giving an attacker the ability to execute arbitrary code within the application context.

Attack Vector Breakdown

• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: Required
• Scope: Unchanged
• Confidentiality: High
• Integrity: High
• Availability: High

Impact Analysis

This vulnerability is exploitable over the network, meaning any system reachable via the internet or internal network is potentially at risk without physical access. The attack complexity is low, meaning exploitation does not depend on specialized conditions or race windows. Successful exploitation can result in full confidentiality breach (complete data disclosure), complete integrity compromise (data modification or code execution), total availability loss (denial of service). The application allows user input to be interpreted as code, giving an attacker the ability to execute arbitrary code within the application context.

Exploitation Probability (EPSS): 57.4% chance of exploitation in the next 30 days (98th percentile). This places the vulnerability in the highest risk tier — immediate action is critical.

Is CVE-2009-0556 being exploited?

Yes. CVE-2009-0556 is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, restricted to CVEs with confirmed active exploitation in the wild. CISA added this vulnerability on 2026-01-07. Inclusion in KEV triggers the patching mandate under BOD 22-01 for U.S. federal civilian agencies, with a remediation deadline of 2026-01-28.

How to fix CVE-2009-0556

Apply the latest security update via Windows Update, WSUS, or Microsoft Update Catalog. For enterprise environments, use SCCM/Intune for managed deployment. If the patch cannot be applied immediately, check the MSRC advisory for workarounds such as registry-based mitigations or disabling affected features. Check the Microsoft Security Response Center page for the specific patch or update. CISA's Known Exploited Vulnerabilities catalog requires U.S. federal agencies to remediate this vulnerability by the due date shown below under Binding Operational Directive 22-01. Private organizations should treat KEV entries as priority-one patches because active exploitation has been confirmed in the wild.

Related Vulnerabilities

Other actively exploited vulnerabilities affecting Office or sharing the same weakness (CWE-94):

• CVE-2009-0238 (High 8.8) [same product + same CWE] — Microsoft Office Excel 2000 SP3, 2002 SP3, 2003 SP3, and 2007 SP1; Excel…
• CVE-2026-21514 (High 7.8) [same product] — Reliance on untrusted inputs in a security decision in Microsoft Office Word…
• CVE-2026-21509 (High 7.8) [same product] — Reliance on untrusted inputs in a security decision in Microsoft Office allows…
• CVE-2007-0671 (High 8.8) [same product] — Unspecified vulnerability in Microsoft Excel 2000, XP, 2003, and 2004 for Mac…
• CVE-2008-4250 (Critical 9.8) [same vendor + same CWE] — The Server service in Microsoft Windows 2000 SP4, XP SP2 and SP3, Server 2003…

Frequently asked questions

Is CVE-2009-0556 critical?

CVE-2009-0556 has a CVSS 3.1 base score of 8.8 — High severity. It should be treated as a priority patch, especially given the active exploitation confirmed by CISA.

Is CVE-2009-0556 being actively exploited?

Yes — CISA added CVE-2009-0556 to the Known Exploited Vulnerabilities catalog on 2026-01-07. Inclusion in KEV means CISA has confirmed in-the-wild exploitation.

How do I patch CVE-2009-0556?

Apply the security update from Microsoft for Office. Federal agencies must remediate by 2026-01-28 under BOD 22-01. Refer to the Microsoft Security Response Center for the official patch.

What type of vulnerability is CVE-2009-0556?

CVE-2009-0556 is classified under CWE-94 (Code Injection). The application allows user input to be interpreted as code, giving an attacker the ability to execute arbitrary code within the application context.

What is the CVSS score for CVE-2009-0556?

CVE-2009-0556 has a CVSS 3.1 base score of 8.8, classifying it as High severity. The attack vector is Network, attack complexity is Low, and no privileges are required.