CVE-2026-80636 in Linux
Summary
by MITRE • 08/28/2026
In the Linux kernel, the following vulnerability has been resolved:
netfilter: conntrack: revert ct extension genid infrastructure
This infrastructure is not used anymore after moving ct timeout and helper to use datapath refcount to track object use.
Revert commit c56716c69ce1 ("netfilter: extensions: introduce extension genid count") this patch disables all ct extensions (leading to NULL) for unconfirmed conntracks, when this is only targeted at ct helper and ct timeout. There is also codebase that dereferences the ct extension without checking for NULL which could lead to crash.
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Analysis
by VulDB Data Team • 08/28/2026
The Linux kernel's netfilter subsystem underwent a significant architectural shift regarding how connection tracking objects are managed, specifically moving from generation ID-based reference counting to datapath refcounting for timeout and helper mechanisms. This transition was intended to improve the efficiency and reliability of object lifecycle management within the network stack. However, an earlier commit introducing extension generation identifier infrastructure failed to align with this new paradigm, creating a mismatch in how connection tracking extensions are handled during different stages of packet processing. The reverted code attempted to disable all connection tracking extensions for unconfirmed connections by setting them to NULL, but this blanket approach inadvertently affected components that were not the intended target, such as general extension handlers rather than just timeout and helper modules.
This misalignment introduces a critical technical flaw where certain parts of the netfilter codebase attempt to dereference connection tracking extension pointers without verifying their validity against null values. Because the reverted infrastructure incorrectly nullified extensions for unconfirmed connections, any subsequent operation that assumes these extensions are present will encounter a NULL pointer dereference. In kernel space, such an error is severe as it bypasses standard user-space safety checks and directly impacts system stability. The immediate operational impact of this vulnerability is a potential kernel panic or system crash when network packets trigger the affected code paths during connection establishment phases where objects remain unconfirmed.
From a classification perspective, this issue aligns with CWE-476, which describes NULL Pointer Dereference vulnerabilities. These occur when software attempts to use a pointer that has not been initialized or has been explicitly set to null without proper validation checks in place. The vulnerability also relates to improper resource management and state handling within the kernel network stack, reflecting weaknesses often categorized under CWE-20 regarding improper input validation of data structures used for internal object tracking.
The attack surface for this flaw is primarily local or remote depending on whether an attacker can influence packet flows that trigger unconfirmed connection states with specific extension dependencies. While exploitation typically requires triggering a crash rather than achieving arbitrary code execution, the resulting denial of service poses a significant risk to system availability and network reliability. Mitigation strategies involve applying the kernel patch that reverts the problematic commit c56716c69ce1, thereby restoring correct behavior where extensions are not indiscriminately nullified for unconfirmed connections. System administrators should ensure their Linux kernels are updated to versions containing this fix, particularly those running netfilter-based firewalling or NAT services that process high volumes of new connection attempts.