CVE-2017-7979 in Linux
Summary
by MITRE
The cookie feature in the packet action API implementation in net/sched/act_api.c in the Linux kernel 4.11.x through 4.11-rc7 mishandles the tb nlattr array, which allows local users to cause a denial of service (uninitialized memory access and refcount underflow, and system hang or crash) or possibly have unspecified other impact via "tc filter add" commands in certain contexts. NOTE: this does not affect stable kernels, such as 4.10.x, from kernel.org.
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Analysis
by VulDB Data Team • 12/01/2022
The vulnerability described in CVE-2017-7979 resides within the Linux kernel's packet action API implementation, specifically in the net/sched/act_api.c file. This flaw affects kernel versions 4.11.x through 4.11-rc7, creating a critical security issue that can be exploited by local attackers to execute denial of service attacks. The vulnerability stems from improper handling of the tb nlattr array during packet filtering operations, which represents a fundamental flaw in the kernel's network traffic control subsystem.
The technical root cause involves the mishandling of the tb nlattr array structure when processing tc filter add commands through the traffic control interface. This improper array management creates conditions where uninitialized memory access can occur, leading to unpredictable behavior within the kernel space. The flaw manifests as a refcount underflow condition that can trigger system instability, resulting in complete system hangs or crashes. The vulnerability operates at the kernel level, making it particularly dangerous as it can compromise the entire system's stability and availability.
From an operational perspective, this vulnerability presents significant risks to systems running affected kernel versions, particularly those utilizing traffic control features for network packet filtering and management. Local users with minimal privileges can exploit this weakness to cause system-wide disruptions, making it a serious concern for server environments and network infrastructure devices that rely on Linux kernel traffic control mechanisms. The impact extends beyond simple denial of service to potentially enabling more sophisticated attacks that could leverage the unstable kernel state for privilege escalation or data corruption.
The vulnerability aligns with CWE-457: Use of Uninitialized Variable, which specifically addresses the improper handling of uninitialized memory that can lead to unpredictable behavior and system instability. Additionally, this issue demonstrates characteristics consistent with ATT&CK technique T1499.001: Endpoint Denial of Service, where adversaries can cause system resources to become unavailable through kernel-level exploits. Organizations using kernel versions 4.11.x through 4.11-rc7 should immediately implement mitigations, including kernel updates to versions that address this specific flaw. The affected kernel versions represent a narrow range that excludes stable releases such as 4.10.x, making version identification critical for proper remediation.
Mitigation strategies should prioritize immediate kernel upgrades to patched versions, as the vulnerability does not affect stable kernel releases. System administrators should also consider implementing network traffic control restrictions to limit exposure, though this approach provides only partial protection. Monitoring for abnormal system behavior or kernel panics should be enhanced to detect potential exploitation attempts. The vulnerability's local privilege requirement means that access control measures and privilege separation remain important defensive strategies, though they cannot prevent exploitation by users with existing system access. Organizations should also verify their kernel versions against the affected ranges and ensure that all systems are updated to versions that contain the necessary patches for this specific memory management flaw.