CVE-2026-80637 in Linux
Summary
by MITRE • 08/28/2026
In the Linux kernel, the following vulnerability has been resolved:
netfilter: synproxy: fix unaligned memory access in timestamp adjustment
Use get_unaligned_be32() and put_unaligned_be32() to safely read and write the timestamp fields. This prevents performance degradation due to unaligned memory access or even a crash on strict alignment architectures.
This follows the implementation of timestamp parsing in the networking stack at tcp_parse_options() and synproxy_parse_options().
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Analysis
by VulDB Data Team • 08/28/2026
The Linux kernel vulnerability identified within the netfilter subsystem specifically affects the SYN proxy functionality, which is responsible for handling TCP handshake packets to protect backend servers from connection exhaustion attacks. The core technical flaw lies in how timestamp options are parsed and manipulated during packet processing. Specifically, the code was performing direct memory accesses on timestamp fields without ensuring that these operations were aligned according to the architecture's requirements. On many modern processor architectures, such as ARM or certain configurations of RISC-V, accessing data structures at unaligned addresses can result in significant performance penalties due to multiple bus cycles being required to fetch the data. In more strict alignment environments, this improper access pattern triggers a hardware exception that leads to an immediate kernel panic or system crash, effectively causing a denial of service condition for any host relying on SYN proxy protection mechanisms.
This issue stems from a lack of adherence to standard practices for handling network protocol headers where field boundaries do not always align with natural word sizes. The timestamp option in TCP packets is variable-length and its position within the header can vary depending on other options present, making it prone to misalignment when accessed directly via pointer casting. By failing to use proper unaligned access primitives, the implementation violated fundamental principles of portable C programming for network stacks. This oversight mirrors similar issues previously addressed in tcp_parse_options(), where robust parsing logic was introduced to handle variable header structures safely. The absence of such safeguards in synproxy_parse_options() created a consistency gap that exposed systems running vulnerable kernel versions to instability under specific traffic patterns involving SYN proxy processing.
From an industry standards perspective, this vulnerability aligns with CWE-1240: Use of Insecure or Deprecated Functionality regarding memory access alignment and CWE-787: Out-of-bounds Write if the misalignment leads to buffer corruption in edge cases, though primarily it is a stability issue related to hardware architecture constraints. It also relates to CWE-693: Protection Mechanism Failure where the kernel fails to prevent an operation that compromises system integrity due to improper implementation of memory access rules. In terms of attack vectors and defensive mapping, this falls under MITRE ATT&CK technique T1498: Network Denial of Service, as an attacker could potentially craft malicious TCP packets with specific option configurations to trigger the unaligned access fault on strict alignment architectures, thereby crashing the host or degrading network performance significantly.
The remediation for this vulnerability involves replacing direct memory reads and writes with architecture-aware functions designed specifically for handling unaligned data. The fix implements get_unaligned_be32() for reading timestamp values and put_unaligned_be32() for writing them back after adjustment. These helper functions abstract the underlying hardware differences, ensuring that bytes are fetched or stored correctly regardless of whether the memory address is naturally aligned to a 32-bit boundary. This approach not only resolves the immediate crash risk but also optimizes performance by avoiding the penalty associated with software-emulated unaligned accesses on architectures where it would otherwise be necessary. It ensures consistency across the networking stack, aligning SYN proxy behavior with established patterns in tcp_parse_options().
To mitigate this vulnerability, system administrators and security operations teams must ensure that all Linux systems running netfilter-based firewalls or load balancers are updated to a kernel version containing this patch. Since SYN proxy is often deployed at network perimeters to defend against TCP SYN flood attacks, the stability of this component is critical for maintaining service availability. Regular vulnerability scanning should include checks for kernel package versions and specific module configurations related to netfilter synproxy. Additionally, monitoring system logs for oops messages or panic traces associated with networking modules can help identify instances where unpatched systems may have experienced transient failures due to this flaw before the update was applied.