CVE-2008-2750 in Linux
Summary
by MITRE
The pppol2tp_recvmsg function in drivers/net/pppol2tp.c in the Linux kernel 2.6 before 2.6.26-rc6 allows remote attackers to cause a denial of service (kernel heap memory corruption and system crash) and possibly have unspecified other impact via a crafted PPPOL2TP packet that results in a large value for a certain length variable.
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Analysis
by VulDB Data Team • 08/14/2019
The vulnerability identified as CVE-2008-2750 represents a critical heap memory corruption flaw within the Linux kernel's PPP over L2TP implementation. This issue affects kernel versions prior to 2.6.26-rc6 and specifically targets the pppol2tp_recvmsg function located in drivers/net/pppol2tp.c. The flaw arises from insufficient input validation when processing PPPOL2TP packets, creating a scenario where remote attackers can manipulate packet structures to trigger memory corruption. The vulnerability operates through a carefully crafted packet that forces the length variable to assume an unexpectedly large value, ultimately leading to kernel heap corruption and system instability.
The technical exploitation of this vulnerability demonstrates a classic buffer overflow condition within kernel space memory management. When the pppol2tp_recvmsg function processes incoming PPPOL2TP packets, it fails to properly validate the length parameter contained within the packet headers. This validation gap allows an attacker to construct a malicious packet where the length field contains a value that exceeds the expected bounds for kernel heap allocation. The resulting memory corruption manifests as heap corruption in kernel memory space, which can lead to unpredictable behavior including kernel panics, system crashes, and complete denial of service conditions. The vulnerability's impact extends beyond simple DoS, as the heap corruption may potentially enable more sophisticated attacks depending on the system's memory state and the specific nature of the corruption.
From an operational perspective, this vulnerability presents significant risks to network infrastructure relying on Linux-based systems with PPPOL2TP support. The remote attack vector means that any system processing PPPOL2TP traffic is potentially exposed to exploitation without requiring local access or authentication. Network administrators responsible for maintaining VPN services, remote access solutions, or any system utilizing PPPOL2TP protocols face critical exposure risks. The vulnerability's potential for system crashes can disrupt critical network services, particularly in environments where continuous availability is essential. Additionally, the unspecified other impacts mentioned in the original description suggest the possibility of information disclosure or privilege escalation scenarios, though these remain unconfirmed. The vulnerability affects systems that implement the Linux kernel's L2TP protocol support, making it relevant to a broad range of network infrastructure components including routers, firewalls, and dedicated VPN appliances.
The mitigation strategy for CVE-2008-2750 centers on immediate kernel version upgrades to 2.6.26-rc6 or later releases where the vulnerability has been addressed through proper input validation. System administrators should prioritize patching affected systems, particularly those handling PPPOL2TP traffic or serving as network gateways. Network segmentation and access control measures can provide additional defense in depth, limiting exposure by restricting access to systems that require PPPOL2TP functionality. Monitoring for anomalous network traffic patterns and potential exploitation attempts should be implemented, as the vulnerability may manifest through specific packet structures that could be detected by intrusion detection systems. Organizations should also consider disabling PPPOL2TP functionality on systems where it is not required, reducing the attack surface. The fix implemented in the patched kernel versions addresses the root cause by introducing proper bounds checking on the length variable, preventing the exploitation scenario that leads to heap corruption. This vulnerability aligns with CWE-121, Heap-based Buffer Overflow, and represents a typical example of how improper input validation in kernel space can lead to catastrophic system failures, demonstrating the critical importance of robust memory management practices in operating system kernels.