Microsoft DirectX NULL Byte Overwrite
CVE-2009-1537 is a high-severity improper neutralization of null byte or NUL character vulnerability in Directx from Microsoft, with a CVSS 2.0 base score of 9.3 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected Directx versions: 7.0; 7.0a; 7.1, and others listed below. The record does not name a fixed version, so check the vendor advisory. CISA added it to the Known Exploited Vulnerabilities catalogue on May 20, 2026, which means attacks have been observed in the wild.
Attackers are already exploiting this vulnerability, according to CISA.
What to do
- Check which version of Directx you run against the affected versions below, and install the vendor's latest release.
- 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.
- Read the advisory on blogs.technet.com for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Microsoft | Directx | 7.0; 7.0a; 7.1; 8.1; 8.1b; 9.0; 9.0a; 9.0b; and 1 more ranges | Not stated |
| Microsoft | Windows 2000 | Not specified in the record | Not stated |
| Microsoft | Windows 2003 Server | Not specified in the record | Not stated |
| Microsoft | Windows Server 2003 | Not specified in the record | Not stated |
| Microsoft | Windows Xp | Not specified in the record | Not stated |
Version data comes from NVD's product matching. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Access vector
- NetworkCan be exploited remotely over a network.
- Access complexity
- MediumSome conditions must be met.
- Authentication
- NoneNo login is needed.
- Confidentiality
- CompleteAll data can be read.
- Integrity
- CompleteAny data can be modified.
- Availability
- CompleteThe system can be shut down completely.
Vector: AV:N/AC:M/Au:N/C:C/I:C/A:C. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 8.8 | High | CISA (ADP) |
| CVSS 2.0 | 9.3 | High | NVD |
Official description
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."
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Neutralization of Null Byte or NUL Character
The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes NUL characters or null bytes when they are sent to a downstream component.
How developers prevent this class of flaw
- Developers should anticipate that null characters or null bytes will be injected/removed/manipulated in the input vectors of their product. Use an appropriate combination of denylists and allowlists to ensure only valid, expected and appropriate input is processed by the system.
- Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.
More Improper Neutralization of Null Byte or NUL Character vulnerabilities (CWE-158)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: active, automatable: no, technical impact: total).
- Added to CISA's Known Exploited Vulnerabilities catalogue.
- Deadline for US federal agencies to remediate, set by CISA.
- Record last changed materially (score, affected products, status or references).
References
Advisories
- blogs.technet.com/msrc/archive/2009/05/28/microsoft-security-advisory-971778-vulnerability-in-microsoft-direc…
- blogs.technet.com/srd/archive/2009/05/28/new-vulnerability-in-quicktime-parsing.aspx
- secunia.com/advisories/35268
- microsoft.com/technet/security/advisory/971778.mspx
- vupen.com/english/advisories/2009/1445
- vupen.com/english/advisories/2009/1886
- docs.microsoft.com/en-us/security-updates/securitybulletins/2009/ms09-028
Third-party and government advisories
- us-cert.gov/cas/techalerts/TA09-195A.htmlUS Government Resource
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2009-1537US Government Resource
Other references
- isc.sans.org/diary.html?storyid=6481Not Applicable
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