CVE-2009-2695 in Linux
Summary
by MITRE
The Linux kernel before 2.6.31-rc7 does not properly prevent mmap operations that target page zero and other low memory addresses, which allows local users to gain privileges by exploiting NULL pointer dereference vulnerabilities, related to (1) the default configuration of the allow_unconfined_mmap_low boolean in SELinux on Red Hat Enterprise Linux (RHEL) 5, (2) an error that causes allow_unconfined_mmap_low to be ignored in the unconfined_t domain, (3) lack of a requirement for the CAP_SYS_RAWIO capability for these mmap operations, and (4) interaction between the mmap_min_addr protection mechanism and certain application programs.
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Analysis
by VulDB Data Team • 08/20/2021
The vulnerability described in CVE-2009-2695 represents a critical privilege escalation flaw in the Linux kernel affecting versions prior to 2.6.31-rc7. This issue stems from insufficient protection mechanisms that permit memory mapping operations targeting page zero and other low memory addresses, creating a pathway for local attackers to exploit NULL pointer dereference vulnerabilities. The flaw operates at the kernel level and specifically targets the memory management subsystem's handling of mmap operations, making it particularly dangerous as it can be leveraged by unprivileged users to elevate their privileges within the system.
The technical implementation of this vulnerability involves multiple interconnected weaknesses that compound the risk. The primary issue manifests through the default configuration of the allow_unconfined_mmap_low boolean in SELinux on Red Hat Enterprise Linux 5, which inadvertently permits dangerous memory mapping operations. Additionally, a critical error exists where the allow_unconfined_mmap_low setting is ignored within the unconfined_t domain, effectively nullifying security controls that should prevent these operations. The vulnerability also lacks proper capability requirements, specifically the CAP_SYS_RAWIO capability, which should normally be mandatory for such dangerous mmap operations. This absence means that any local process can potentially perform these operations without proper authorization, creating a fundamental breach in the kernel's security model.
The operational impact of CVE-2009-2695 is severe and far-reaching within affected systems. Local attackers can exploit this vulnerability to gain elevated privileges, potentially transitioning from regular user accounts to root access. This privilege escalation allows malicious actors to execute arbitrary code with system-level privileges, modify critical system files, establish persistent backdoors, and compromise the integrity of the entire operating system. The vulnerability's exploitation is particularly concerning because it requires minimal user interaction and can be automated, making it attractive to both casual attackers and sophisticated threat actors. The interaction between the mmap_min_addr protection mechanism and certain application programs further compounds the risk, as legitimate applications may inadvertently trigger the vulnerability conditions.
Security mitigations for this vulnerability must address the fundamental kernel-level flaw through immediate system updates to kernel versions 2.6.31-rc7 or later where the issue has been resolved. Organizations should implement comprehensive patch management procedures to ensure all systems are updated promptly. Additionally, system administrators should review and tighten SELinux policies to disable the allow_unconfined_mmap_low boolean setting, particularly in environments where security is paramount. The implementation of proper capability requirements for mmap operations should be enforced through kernel configuration changes and security modules. Monitoring systems should be enhanced to detect unusual mmap operations targeting low memory addresses, and regular security audits should verify that proper security controls remain in place. This vulnerability aligns with CWE-121 and CWE-122 categories related to buffer overflow conditions and improper access control, while its exploitation patterns correspond to ATT&CK techniques involving privilege escalation through kernel vulnerabilities and local execution of malicious code.
The broader implications of this vulnerability extend beyond immediate exploitation, as it highlights systemic weaknesses in kernel security design and the importance of proper privilege separation. The flaw demonstrates how seemingly minor configuration issues can create significant security risks when combined with other kernel-level vulnerabilities. System administrators must understand that this vulnerability represents not just a single point of failure but a potential gateway for complete system compromise. The remediation process requires careful consideration of system compatibility and the potential impact of kernel updates on existing applications. Organizations should also implement layered security approaches that include intrusion detection systems, proper logging of memory operations, and regular security assessments to identify similar vulnerabilities that may exist in other system components.