CVE-2009-1123
Microsoft Windows Improper Input Validation Vulnerability
Description
CVE-2009-1123 is a HIGH severity privilege escalation vulnerability in the Microsoft Windows kernel affecting Windows 2000, Windows XP, Windows Vista, Windows Server 2003, and Windows Server 2008. The flaw arises because the kernel does not properly validate changes to unspecified kernel objects, allowing a local attacker who can convince a user to run a crafted application to gain elevated SYSTEM-level privileges on the target machine. This vulnerability is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog with a remediation deadline of March 24, 2022, confirming that it has been actively exploited in real-world attacks. With an EPSS score of 0.04295 (88.7th percentile), the vulnerability demonstrates a notable exploitation probability that places it well above the median for all tracked CVEs, though it is not associated with any known ransomware campaigns.
KEV Information
CVSS Score
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:HOpen in CalculatorAffected Products
| Vendor | Product | Version |
|---|---|---|
| microsoft | windows 2000 | - |
| microsoft | windows server 2003 | - |
| microsoft | windows server 2008 | - |
| microsoft | windows vista | - |
| microsoft | windows xp | - |
Multiple CVSS Assessments
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
References
- http://osvdb.org/54940(Broken Link)
- http://secunia.com/advisories/35372(Broken Link)
- http://www.securitytracker.com/id?1022359(Broken Link, Third Party Advisory, VDB Entry)
- http://www.us-cert.gov/cas/techalerts/TA09-160A.html(Broken Link, Third Party Advisory, US Government Resource)
- http://www.vupen.com/english/advisories/2009/1544(Broken Link)
- https://docs.microsoft.com/en-us/security-updates/securitybulletins/2009/ms09-025(Patch, Vendor Advisory)
- https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A6206(Broken Link)
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2009-1123(US Government Resource)
Weakness Type
Improper Input Validation in Kernel Objects
Improper input validation vulnerabilities occur when software fails to correctly verify or sanitize data before using it in security-critical operations. In the context of operating system kernels, this class of weakness is particularly dangerous because the kernel operates at the highest privilege level and manages all system resources. When kernel code accepts malformed or unexpected input without adequate checks, attackers can manipulate internal data structures to subvert security boundaries, escalate privileges, or execute arbitrary code in kernel mode.
In the case of CVE-2009-1123, the Microsoft Windows kernel does not properly validate modifications to certain kernel objects. This means a locally executing application can pass crafted data to kernel interfaces that alter internal object state in unintended ways. Because kernel objects govern process tokens, security descriptors, and access control decisions, corrupting these objects allows an attacker to elevate their privileges from a standard user context to SYSTEM. The attack requires local access and user interaction (running a malicious application), but once triggered it provides complete control over the affected system. Learn more about input validation weaknesses at CWE resources on MITRE.
Impact Analysis
CVE-2009-1123 carries a CVSS 3.1 score of 7.8 (HIGH) with an Unchanged scope, reflecting severe local impact across all three security dimensions when exploited.
Confidentiality (High): Successful exploitation grants the attacker SYSTEM-level privileges, providing unrestricted read access to all data on the affected machine. This includes password hashes stored in the Security Account Manager (SAM) database, cached credentials, encryption keys, and any files protected by user-level access controls. An attacker operating with SYSTEM privileges can access data belonging to all user accounts on the system, making confidentiality impact comprehensive.
Integrity (High): With SYSTEM privileges, an attacker can modify any file, registry key, or system configuration on the affected host. This includes the ability to install rootkits, modify security policies, create new administrator accounts, tamper with audit logs to conceal malicious activity, and alter system binaries. The integrity of the entire operating system and all hosted applications is compromised once SYSTEM access is achieved.
Availability (High): Full system control enables an attacker to disrupt any service running on the machine, corrupt critical system files rendering the OS unbootable, or deploy destructive payloads. The attacker could also leverage the elevated access to disable security tools, terminate critical processes, or encrypt data for extortion purposes.
Scope (Unchanged): The scope remains unchanged because the privilege escalation occurs within the Windows operating system itself rather than crossing a security boundary into a different component. However, the escalation from user to SYSTEM effectively removes all access restrictions within the OS. With an EPSS score of 0.04295 at the 88.7th percentile, this vulnerability has demonstrated real-world exploitation activity that exceeds the vast majority of cataloged vulnerabilities.
Exploit Maturity
Active Exploitation: CVE-2009-1123 is confirmed to have been actively exploited in the wild. Its inclusion in CISA's Known Exploited Vulnerabilities (KEV) catalog as of March 3, 2022, reflects documented evidence of real-world attacks leveraging this kernel privilege escalation flaw. The vulnerability has been known since 2009, giving threat actors many years to develop and refine exploit techniques targeting unpatched legacy systems.
Ransomware Association: CISA's KEV entry does not indicate a known association with ransomware campaigns for this specific vulnerability. However, privilege escalation vulnerabilities in Windows kernels are commonly used as secondary exploitation steps in ransomware attack chains to gain the elevated access necessary for encrypting files system-wide and disabling security products.
Public Exploits: While the original vulnerability disclosure dates to June 2009 as part of Microsoft's security bulletin MS09-025, exploit information has been circulating through security research channels. References from US-CERT (TA09-160A) and multiple vulnerability databases confirm the availability of technical details that lower the barrier to exploitation.
EPSS Context: The EPSS score of 0.04295 places this vulnerability at the 88.7th percentile, meaning it has a higher predicted exploitation probability than approximately 89% of all scored vulnerabilities. This elevated score is consistent with its KEV catalog inclusion and reflects the ongoing risk from unpatched legacy Windows systems.
KEV Remediation Deadline: CISA set a federal remediation deadline of March 24, 2022, requiring all federal civilian agencies to have applied patches or mitigations by that date. Organizations still running affected Windows versions without patches remain at elevated risk.
Remediation
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Apply Microsoft security update MS09-025 immediately. This critical security bulletin released in June 2009 addresses CVE-2009-1123 along with related kernel vulnerabilities. Install the appropriate update for your Windows version (Windows 2000, XP, Vista, Server 2003, or Server 2008) from the Microsoft Update Catalog or through Windows Update.
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Upgrade legacy Windows systems to supported versions. Windows 2000, Windows XP, and Windows Vista have long since reached end of support and no longer receive security updates. Migrate these systems to a currently supported Windows version such as Windows 10 or Windows 11 to benefit from ongoing security patches and modern kernel hardening features like Kernel Data Protection and Virtualization-Based Security.
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Restrict local user access and enforce least privilege. Since exploitation requires local access and a user running a crafted application, limit which users can log on to affected systems and enforce application whitelisting policies to prevent execution of unauthorized programs. Use Group Policy or Microsoft AppLocker to restrict executable files to trusted applications only.
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Deploy endpoint detection and response (EDR) solutions. Modern EDR tools can detect privilege escalation attempts by monitoring for suspicious kernel object manipulation, unexpected token modification, and process privilege changes. Ensure EDR agents are deployed on all systems, including legacy hosts that cannot be immediately upgraded.
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Segment networks containing legacy Windows systems. Isolate systems running end-of-life Windows versions into dedicated network segments with strict firewall rules limiting inbound and outbound connections. This containment strategy reduces the blast radius if a legacy system is compromised through this or similar kernel vulnerabilities.
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Audit systems for indicators of prior compromise. Given that this vulnerability has been actively exploited since 2009, conduct forensic analysis on affected systems to check for signs of past exploitation such as unexpected SYSTEM-level processes, unauthorized local accounts, modified system binaries, or suspicious scheduled tasks.
Technical Details
CVE-2009-1123 is a local privilege escalation vulnerability in the Microsoft Windows kernel caused by improper validation of changes to kernel objects. The kernel, which operates at Ring 0 in the x86 privilege model, manages all operating system resources through internal data structures known as kernel objects. These objects represent processes, threads, tokens, and other OS primitives that govern security enforcement and resource access.
The vulnerability exists because the kernel fails to properly validate modifications to certain kernel objects when processing requests from user-mode applications. An attacker can craft an application that makes specific system calls to manipulate these objects in ways that the kernel does not anticipate or properly restrict. By corrupting or modifying security-sensitive kernel objects such as process tokens or security descriptors, the attacker can elevate their process privileges from a standard user context to SYSTEM.
The CVSS 3.1 vector (AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H) indicates that while the attack vector is local (requiring code execution on the target), the attack complexity is low once local access is achieved. User interaction is required because the victim must execute the attacker's crafted application. The scope is unchanged, meaning the impact stays within the Windows OS security boundary, but the resulting SYSTEM privileges provide complete control over all three security dimensions.
The root cause is insufficient validation logic in the kernel's object management subsystem, a common pattern in legacy Windows kernel code that predates modern security development lifecycle practices. Microsoft addressed this in the MS09-025 bulletin by adding proper validation checks to the affected kernel code paths.
Frequently Asked Questions
What is CVE-2009-1123?
CVE-2009-1123 is a privilege escalation vulnerability in the Microsoft Windows kernel that allows local users to gain SYSTEM-level privileges by running a specially crafted application. The flaw stems from the kernel's failure to properly validate changes to internal kernel objects, enabling manipulation of security-critical data structures. It affects Windows 2000, Windows XP, Windows Vista, Windows Server 2003, and Windows Server 2008, and was patched in Microsoft's June 2009 security bulletin MS09-025.
Which systems are affected by CVE-2009-1123?
CVE-2009-1123 affects Microsoft Windows 2000, Windows XP, Windows Vista, Windows Server 2003, and Windows Server 2008. All service pack levels of these operating systems are potentially vulnerable if the MS09-025 security update has not been applied. Since all of these Windows versions have reached end of support, any systems still running them without the patch remain permanently vulnerable to this exploit. Organizations should prioritize migration to supported Windows versions.
How severe is CVE-2009-1123?
CVE-2009-1123 has a CVSS 3.1 score of 7.8 (HIGH) and is listed in CISA's Known Exploited Vulnerabilities catalog, confirming active real-world exploitation. Its EPSS score of 0.04295 places it at the 88.7th percentile for predicted exploitation likelihood. While the vulnerability requires local access and user interaction, successful exploitation grants complete SYSTEM-level control over the affected machine, making it a serious threat particularly on unpatched legacy systems.
How do I remediate CVE-2009-1123?
The primary remediation is applying Microsoft security update MS09-025, which was released in June 2009. For Windows systems still running affected versions, install the update from the Microsoft Update Catalog. However, since all affected operating systems (Windows 2000, XP, Vista, Server 2003, Server 2008) have reached end of support, the recommended long-term remediation is upgrading to a currently supported Windows version. In the interim, restrict local user access, enforce application whitelisting, deploy endpoint detection solutions, and network-segment any legacy systems that cannot be immediately upgraded.
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