CVE-2019-20785: 
NixOS vulnerability analysis and mitigation

A vulnerability was discovered in the Linux kernel versions 4.17 through 5.0rc6, identified as CVE-2019-8956. The issue exists in the SCTP (Stream Control Transmission Protocol) implementation, specifically in the sctp_sendmesg() function, where improper handling of association list corruption could occur (Openwall).

The vulnerability stems from a logic error in the sctp_sendmesg() function. When walking the list of endpoint associations, the association can be dropped from the list, leading to list corruption. The issue was introduced by commit 4910280503f3 which added support for the SCTP_SENDALL flag process in sendmsg (Openwall).

This vulnerability could allow local attackers to escalate privileges to root level on affected systems, presenting a significant security risk to Linux systems running the vulnerable kernel versions (Openwall).

The vulnerability requires local access to the system to exploit, as it affects the SCTP implementation in the Linux kernel. It has been confirmed as a local root exploit, making it particularly dangerous for multi-user systems (Openwall).

The fix involves using list_for_each_entry_safe() instead of the previous implementation to properly handle cases where associations are dropped from the list. Systems should be updated to a patched kernel version that includes this fix (Openwall).