CVE-2009-0556: Microsoft Office

Should you act?

Exploited: patch now if you run it

CISA has confirmed exploitation in the wild. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

Yes, if you run Microsoft Office. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2026-01-07, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2026-01-28; treat that as the outer limit, not the target.
EPSS 67.3%, percentile 99: FIRST’s model estimates a 67.3% chance of exploitation activity in the next 30 days, higher than 99% of all scored CVEs (very high). EPSS is a probability, not a verdict.
Needs a user to click or open something. Phishing makes that realistic, but it is not wormable.

What it is

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."

CISA’s summary

Microsoft Office PowerPoint contains a code injection vulnerability that allows remote attackers to execute arbitrary code via a PowerPoint file with an OutlineTextRefAtom containing an invalid index value that triggers memory corruption.

Weakness type: CWE-94.

Product: Microsoft Office · Assigned by: microsoft · Published: 2009-04-03

Affected and fixed versions

Vendor	Product	Affected versions (per CVE record)
n/a	n/a	see vendor advisory

Severity scores

Scored by	CVSS	Score	Vector
CISA-ADP	3.1	8.8 High	`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H`

Attack vector: network (remotely reachable)
Attack complexity: low
Privileges required: none (no login)
User interaction: required (a user must click/open something)
Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

CISA KEV: added 2026-01-07; federal due date 2026-01-28. Known ransomware use: Unknown.
CISA required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
CISA SSVC assessment: exploitation active, automatable no, technical impact total.
FIRST EPSS (model of 2026-10-21): 67.31% probability of exploitation activity in the next 30 days; percentile 99.

Timeline

2009-04-03 — CVE record published by microsoft
2026-01-07 — Added to CISA’s Known Exploited Vulnerabilities catalog
2026-01-08 — CVE record last updated
2026-01-28 — CISA remediation deadline for US federal agencies

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Should you act?

What it is

CISA’s summary

Affected and fixed versions

Severity scores

Exploitation and urgency

Timeline

Sources and references

Vendor and project advisories, patches

Vulnerability records

Government

Other references from the CVE record and advisory