CVE-2011-2525 in Linux
Summary
by MITRE
The qdisc_notify function in net/sched/sch_api.c in the Linux kernel before 2.6.35 does not prevent tc_fill_qdisc function calls referencing builtin (aka CQ_F_BUILTIN) Qdisc structures, which allows local users to cause a denial of service (NULL pointer dereference and OOPS) or possibly have unspecified other impact via a crafted call.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 11/29/2021
The vulnerability described in CVE-2011-2525 resides within the Linux kernel's traffic control subsystem, specifically in the qdisc_notify function located in net/sched/sch_api.c. This flaw affects kernel versions prior to 2.6.35 and represents a critical security issue that demonstrates a failure in proper input validation and access control mechanisms. The vulnerability stems from insufficient validation of qdisc structure references, allowing malicious local users to exploit a path that leads to improper handling of builtin Qdisc structures.
The technical implementation of this vulnerability occurs when the tc_fill_qdisc function is called with references to builtin Qdisc structures that should be protected from direct user access. The qdisc_notify function fails to properly validate these references, creating a condition where a crafted system call can trigger a NULL pointer dereference. This type of vulnerability falls under CWE-476 which specifically addresses NULL pointer dereference conditions, and represents a classic case of improper validation of input parameters within kernel space operations.
The operational impact of this vulnerability extends beyond simple denial of service conditions, though that remains the primary concern. When exploited, the vulnerability can cause kernel oops conditions which result in system crashes and complete system instability. The local privilege escalation potential exists because the vulnerability allows an attacker with minimal privileges to execute arbitrary kernel code paths that should remain protected. This creates an attack surface that can be leveraged for more sophisticated attacks including privilege escalation or persistent system compromise.
From a cybersecurity perspective, this vulnerability demonstrates the critical importance of proper kernel space input validation and access control mechanisms. The ATT&CK framework would categorize this under privilege escalation techniques where local users can leverage kernel vulnerabilities to gain elevated privileges. The vulnerability also aligns with the concept of kernel exploitation patterns where improper validation leads to memory corruption and system instability. Organizations should prioritize patch management for this vulnerability and implement monitoring for suspicious network control operations that might indicate exploitation attempts.
The fix for this vulnerability required modifications to the qdisc_notify function to properly validate qdisc structure references and prevent access to builtin Qdisc structures from user-space applications. This represents a fundamental security principle of least privilege enforcement at kernel boundaries, ensuring that user-space applications cannot directly manipulate kernel data structures that should remain protected. The patch implementation demonstrates the importance of maintaining proper access controls even within kernel subsystems that are designed to be exposed to user-space applications.