FreeBSD Security Advisory - While processing acknowledgements, the RACK code uses several linked lists to maintain state entries. A malicious attacker can cause the lists to grow unbounded. This can cause an expensive list traversal on every packet being processed, leading to resource exhaustion and a denial of service. An attacker with the ability to send specially crafted TCP traffic to a victim system can degrade network performance and/or consume excessive CPU by exploiting the inefficiency of traversing the potentially very large RACK linked lists with relatively small bandwidth cost.
85f2ffcf89eae31c9b0babd62b1d66ae80b60a35fc0e3d2f7a258259db7a0affNetflix has identified several TCP networking vulnerabilities in FreeBSD and Linux kernels. The vulnerabilities specifically relate to the minimum segment size (MSS) and TCP Selective Acknowledgement (SACK) capabilities. The most serious, dubbed _"SACK Panic_," allows a remotely-triggered kernel panic on recent Linux kernels. There are patches that address most of these vulnerabilities. If patches can not be applied, certain mitigations will be effective.
2842c96d7b20ef5dfb0f2ea06c76a1334026b1cbd1953a2b31793af5c8fa3ba7FreeBSD Security Advisory - TCP connections transitioning to the LAST_ACK state can become permanently stuck due to mishandling of protocol state in certain situations, which in turn can lead to accumulated consumption and eventual exhaustion of system resources, such as mbufs and sockets.
ca370532c669a959a43a27961c0f51adab4f5da48a536d4759a39ad719cbe9a9FreeBSD Security Advisory - FreeBSD may add a reassemble queue entry on the stack into the segment list when the reassembly queue reaches its limit. The memory from the stack is undefined after the function returns. Subsequent iterations of the reassembly function will attempt to access this entry. An attacker who can send a series of specifically crafted packets with a connection could cause a denial of service situation by causing the kernel to crash. Additionally, because the undefined on stack memory may be overwritten by other kernel threads, while extremely difficult, it may be possible for an attacker to construct a carefully crafted attack to obtain portion of kernel memory via a connected socket. This may result in the disclosure of sensitive information such as login credentials, etc. before or even without crashing the system.
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