CVE-2022-48748 in Linux
Summary
by MITRE • 06/20/2024
In the Linux kernel, the following vulnerability has been resolved:
net: bridge: vlan: fix memory leak in __allowed_ingress
When using per-vlan state, if vlan snooping and stats are disabled, untagged or priority-tagged ingress frame will go to check pvid state. If the port state is forwarding and the pvid state is not learning/forwarding, untagged or priority-tagged frame will be dropped but skb memory is not freed. Should free skb when __allowed_ingress returns false.
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Analysis
by VulDB Data Team • 03/24/2025
The vulnerability identified as CVE-2022-48748 resides within the Linux kernel's networking subsystem, specifically within the bridge netfilter module's vlan handling functionality. This memory leak occurs in the __allowed_ingress function which manages ingress frame processing for bridge ports with per-vlan state enabled. The issue manifests when vlan snooping and statistics are disabled, creating a scenario where untagged or priority-tagged frames must be evaluated against port and pvid state configurations. The vulnerability represents a classic memory management flaw that can lead to progressive resource exhaustion over time.
The technical root cause involves improper memory deallocation within the bridge vlan processing pipeline. When ingress frames are processed through the __allowed_ingress function, the kernel fails to properly free the socket buffer (skb) memory when the function returns false. This occurs specifically in scenarios where port state is forwarding but the pvid state is not in learning or forwarding mode, causing frames to be dropped but the associated memory allocation to remain unreleased. The flaw exists in the conditional logic path where frame dropping occurs without corresponding memory cleanup operations, creating a memory leak that accumulates with each affected frame processing event.
The operational impact of this vulnerability extends beyond simple memory consumption issues to potentially affect system stability and performance. While individual frame processing may appear benign, sustained operation with high frame traffic volumes can lead to progressive memory exhaustion that impacts overall system performance. The leak occurs during normal network operations when per-vlan state is configured, making it particularly concerning for network infrastructure devices that rely heavily on bridge functionality. Attackers could potentially exploit this to cause denial of service conditions through memory exhaustion, though the direct attack surface is limited to systems actively using the affected bridge vlan configurations.
This vulnerability maps to CWE-401: "Improper Release of Memory" and aligns with ATT&CK technique T1499.001: "File System Wipe: Disk Content Wipe" through potential system instability caused by resource exhaustion. The fix implemented addresses the specific memory management issue by ensuring that socket buffer memory is properly freed when __allowed_ingress returns false, regardless of the frame processing outcome. This remediation follows standard kernel security practices for memory management and aligns with the principle of least privilege in resource handling. The fix requires minimal code changes and maintains backward compatibility while addressing the core memory leak without disrupting existing network functionality.
The vulnerability demonstrates the complexity of memory management in kernel space networking code where multiple state conditions must be properly handled. The issue highlights the importance of comprehensive testing for resource cleanup paths in kernel modules, particularly in high-frequency processing loops. Systems utilizing bridge networking with per-vlan state configurations should be prioritized for patching, as the vulnerability can persist through system uptime and accumulate memory leaks over time. The fix ensures proper resource accounting and prevents the accumulation of unreleased memory that could eventually impact system responsiveness and stability, particularly in environments with high network traffic volumes.