Threats / Microsoft / CVE-2009-3129
CVE-2009-3129
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-06-22
Microsoft Excel vulnerability
Microsoft Excel processes FEATHEADER records with invalid cbHdrData size values, causing pointer offset corruption that enables arbitrary code execution when opening malicious spreadsheets.
Verdict
Today item — known-exploited.
Remote attackers can execute arbitrary code by crafting spreadsheets with malformed FEATHEADER records. The vulnerability affects pointer arithmetic in Excel's record parsing, allowing code injection without user interaction beyond opening a file.
01
Is it exploitable?
— the evidence, ranked above the scoreReported exploitation
10 independent public reports of in-the-wild exploitation are cataloged.Distinct reporting sources (vendor, incident response, government); open them for the underlying claims.
Exploited in the wild
Listed in the CISA Known Exploited Vulnerabilities catalog (added 2022-03-03).
Probability (EPSS)
EPSS 0.85731 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
Severity / affected
Affected: Microsoft, Excel. Confirm exact fixed builds in the vendor advisory.
Weakness (CWE)
Mapped to CWE-94 Code Injection — weakness family: Injection.CWE assignment from the public NVD record; the weakness class drives how the flaw is exploited.
02
Who’s exploiting it?
— attribution turns risk into urgencyAttribution not established
No confirmed (advisory-backed) threat-actor attribution is established for this record. Absence of a named actor is not absence of compromise — see Coverage & confidence.
03
Why it matters
— the attack path, told twice: adversary, then board1
Front door — unauthenticated access narrative 1
Attacker
I craft a spreadsheet file with a FEATHEADER record containing an invalid cbHdrData size element.
Business
An employee receives and opens the malicious spreadsheet, potentially via email or file share.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
I trigger Excel to parse the malformed record, causing a pointer offset calculation error during header data processing.
Business
Excel's memory management becomes corrupted, creating exploitable conditions within the application process.
3
Lateral reach — past segmentation narrative 3
Attacker
I inject and execute arbitrary code within the context of the Excel process on the target system.
Business
The attacker gains code execution with the privileges of the user running Excel, enabling data theft, lateral movement, or system compromise.
04
What to do
— defensible action- Remediate per the vendor advisory — confirm the fixed build for your version and verify exposure.1
Say it to the boardA vulnerability with this evidence profile is a defensible budget line, not a backlog ticket — fund the change against the proof above.
05