CVE-2009-1537
CVE-2009-1537 is a security flaw in Microsoft DirectX. Attackers can run their own code on Microsoft DirectX. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 20 May 2026.[1]
Microsoft DirectX is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff. Microsoft has published a fix or advice.
Description
CISA calls it an NULL byte overwrite in Microsoft DirectX. In its words: “Microsoft DirectX contains a NULL byte overwrite vulnerability in the QuickTime Movie Parser Filter in quartz.dll in DirectShow which could allow remote attackers to execute arbitrary code via a crafted QuickTime media file.”[1]
The CVE record adds: “Unspecified vulnerability in the QuickTime Movie Parser Filter in quartz.dll in DirectShow in Microsoft DirectX 7.0 through 9.0c on Windows 2000 SP4, Windows XP SP2 and SP3, and Windows Server 2003 SP2 allows remote attackers to execute arbitrary code via a crafted QuickTime media file, as exploited in the wild in May 2009, aka "DirectX NULL Byte Overwrite Vulnerability."”[2]
The underlying weakness is CWE-158, in MITRE’s list of common software weaknesses.
It scores 8.8 out of 10 on the Common Vulnerability Scoring System, which rates it high, scored by the organisation that published the CVE using CVSS 3.1.[2]
Affected versions
NVD’s record doesn’t list version ranges for it; Microsoft’s advisory has them[3]. CISA names the product as Microsoft DirectX.
Most families won’t have Microsoft DirectX; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 20 May 2026, 6,200 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 3 Jun 2026 to fix it.[1]
FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 51%. That’s in the top 2% of the flaws it scores.[4]
CISA assesses it as not automatable: each attack takes some work.
CISA doesn’t say who was attacked, or how.
Fix
Microsoft has published a fix or advice.[3] CISA’s 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.”[1]
- Check whether you use it.Microsoft DirectX is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
- Send this page to your IT person.Ask them to confirm it’s fixed, or not in use. CISA gave US government agencies until 3 Jun 2026 to fix it.
- If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.
You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 8.8.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks.[1] | |
| CISA’s deadline for US government agencies to fix it.[1] | |
| FIRST puts the odds of it being used in attacks in the next 30 days at 51%.[4] |
See also
Other Microsoft flaws
- CVE-2026-96951, Microsoft Windows: command injection ·
- CVE-2026-65660, Microsoft SharePoint: code injection ·
- CVE-2026-85880, Microsoft Windows: heap-based buffer overflow ·
- CVE-2026-81963, Microsoft Windows: link following ·
- CVE-2019-1068, Microsoft SQL Server: remote code execution ·
Similar flaws
- CVE-2025-47812, Wing FTP Server: improper neutralization of null byte or NUL character ·
- CVE-2022-1040, Sophos Firewall: authentication bypass ·
Added the same day
- CVE-2026-45498, Microsoft Defender: denial of service ·
- CVE-2026-41091, Microsoft Defender: link following ·
- CVE-2010-0806, Microsoft Internet Explorer: use-after-free ·
- CVE-2010-0249, Microsoft Internet Explorer: use-after-free ·
- CVE-2009-3459, Adobe Acrobat and Reader: heap-based buffer overflow ·
Every Microsoft flaw on CISA’s list · Everything added in May 2026
References
- ^ Cybersecurity and Infrastructure Security Agency. “Microsoft DirectX NULL Byte Overwrite Vulnerability”. Known Exploited Vulnerabilities Catalog, added 20 May 2026.
- ^ National Institute of Standards and Technology. “CVE-2009-1537 Detail”. National Vulnerability Database, published 29 May 2009.
- ^ Microsoft. Advisories and fixes: learn.microsoft.com, docs.microsoft.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.514, percentile 98.9, 31 Oct 2026.
- CVE Program. “CVE-2009-1537”. The official CVE record.
This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.