CVE-2026-74668 in Linux
Summary
by MITRE • 08/22/2026
In the Linux kernel, the following vulnerability has been resolved:
packet: use consistent hard_header_len in TX_RING send path
tpacket_snd() reads dev->hard_header_len independently for skb allocation and header construction in tpacket_fill_skb(). Concurrent netdevice reconfiguration can therefore make the reserved headroom smaller than the amount later pushed, or make copylen - hard_header_len negative.
Snapshot hard_header_len once before processing ring frames and use it for the frame limit, headroom allocation, copy length, and skb construction. Pass the snapshot to tpacket_fill_skb().
The separate SOCK_DGRAM consistency problem between hard_header_len and header_ops->create is not addressed here.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 08/22/2026
This vulnerability addresses a race condition within the Linux kernel's packet socket implementation, specifically affecting the TX_RING send path in the tpacket_snd function. The core issue stems from inconsistent handling of the device structure member hard_header_len during network frame transmission. In the original code logic, the value of dev->hard_header_len was read independently at two distinct stages: first when allocating space for the socket buffer and second when constructing the packet header within tpacket_fill_skb. This lack of atomicity creates a window where concurrent netdevice reconfiguration can alter the hard_header_len value between these two operations. Such race conditions are particularly dangerous in high-throughput network environments or systems with frequent interface state changes, as they undermine the integrity of memory allocation and data structure assumptions made by the kernel networking stack.
The operational impact of this flaw is significant for system stability and security. If a netdevice reconfiguration occurs between the initial read and subsequent usage of hard_header_len, the reserved headroom allocated in the socket buffer may become smaller than the amount actually pushed during header construction. This discrepancy can lead to memory corruption or out-of-bounds writes if the kernel attempts to write beyond the allocated boundaries. Furthermore, the inconsistency can result in a calculation error where copylen minus hard_header_len becomes negative. In C programming and kernel development, treating such values as unsigned integers often leads to massive positive integer overflows, causing excessive data copying that could exhaust system resources or corrupt adjacent memory structures. These conditions effectively create opportunities for denial of service attacks against the host system and potentially privilege escalation if an attacker can exploit the resulting memory corruption to execute arbitrary code within kernel space.
The resolution involves enforcing consistency by snapshotting the hard_header_len value once before processing any frames in the ring buffer. This single, consistent value is then utilized throughout the entire transmission process for determining frame limits, allocating headroom, calculating copy lengths, and constructing the socket buffer. By passing this snapshot to tpacket_fill_skb, the kernel ensures that all subsequent operations rely on a stable representation of the device's header length requirements during that specific transmission context. This approach eliminates the race window by decoupling the allocation logic from dynamic runtime changes in network interface configuration until the current packet processing cycle is complete. It aligns with best practices for handling shared mutable state in concurrent environments, ensuring that internal kernel structures remain consistent throughout a single operation's lifecycle.
From a vulnerability classification perspective, this issue maps to CWE-362, which describes Concurrent Execution using Shared Resource with Improper Synchronization, commonly known as race conditions. The specific mechanism of accessing and modifying data without proper synchronization falls under the broader category of improper lock usage or missing atomicity guarantees in kernel subsystems. In terms of attack vectors, this vulnerability relates to CWE-190, Integer Overflow or Wraparound, due to the potential for negative values being interpreted as large positive integers during length calculations. It also touches upon CWE-787, Out-of-bounds Write, if the headroom miscalculation leads to memory writes beyond allocated buffers. While not directly an ATT&CK technique itself, exploiting this flaw would likely involve techniques associated with Defense Evasion or Privilege Escalation via kernel exploitation, such as leveraging memory corruption for code execution.
Mitigation strategies primarily focus on applying the provided kernel patch that enforces consistent hard_header_len usage. System administrators should ensure their Linux kernels are updated to versions containing this fix. For environments where immediate patching is not feasible, reducing network interface churn and avoiding concurrent configuration changes during high-volume packet transmission can mitigate the risk window. Additionally, enabling strict memory protection mechanisms such as Kernel Page Table Isolation or enforcing SELinux policies may limit the impact of potential exploitation attempts by restricting access to sensitive kernel structures. It is important to note that this fix specifically addresses consistency within the TX_RING send path and does not resolve separate SOCK_DGRAM inconsistencies between hard_header_len and header_ops->create, meaning other related race conditions in different packet socket modes may still require attention or further patches.