CVE-2026-72326 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
net/sched: cake: reject overhead values that underflow length
CAKE accepts signed overhead values and stores them in an s16, but the adjusted packet length calculation uses unsigned arithmetic. A negative effective length can therefore wrap to a large value.
Such configurations make rate accounting depend on integer wraparound rather than on the packet size userspace intended to model. A static netlink lower bound is not enough because packets reaching CAKE can be smaller than any reasonable manual-overhead allowance.
Fold the signed overhead adjustment into the existing datapath MPU clamp so negative adjusted lengths are clamped before link-layer framing adjustments.
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Analysis
by VulDB Data Team • 08/15/2026
This vulnerability resides in the Linux kernel's traffic control subsystem, specifically within the CAKE (CoDel Adaptive Kernel Engine) queuing discipline implementation. The issue stems from a fundamental mismatch between signed and unsigned arithmetic operations during packet length calculations, creating a potential pathway for incorrect rate accounting and traffic shaping behavior.
The core technical flaw involves how CAKE handles overhead values in its packet processing pipeline. When userspace configures CAKE with signed overhead parameters, these values are stored in s16 data types, which can represent negative numbers. However, the subsequent adjusted packet length calculation employs unsigned arithmetic operations, creating a scenario where negative effective lengths can overflow and wrap around to extremely large positive values through integer underflow behavior. This mathematical inconsistency fundamentally breaks the expected relationship between packet sizes and rate accounting mechanisms.
The operational impact of this vulnerability extends beyond simple misbehavior in traffic control calculations. When negative adjusted lengths wrap to large unsigned values, the rate accounting system becomes dependent on integer overflow behavior rather than actual packet sizing that userspace intended to model. This creates unpredictable traffic shaping outcomes where network bandwidth allocation can be dramatically skewed based on how packet sizes interact with the underlying arithmetic overflow conditions. The vulnerability is particularly concerning because it affects the fundamental rate control mechanisms that govern how network traffic is prioritized and managed in real-time applications.
The root cause analysis reveals that a static netlink lower bound configuration is insufficient to prevent this issue, as packets reaching CAKE can legitimately be smaller than any reasonable manual-overhead allowance. This means that even configurations that appear safe from a static configuration perspective can still trigger the underflow condition when processing actual network traffic with varying packet sizes. The solution implemented addresses this by folding the signed overhead adjustment into the existing datapath MPU (Maximum Packet Unit) clamp mechanism, ensuring that negative adjusted lengths are properly clamped before any link-layer framing adjustments occur.
This vulnerability type maps directly to CWE-191, Integer Underflow (Wrap or Wraparound), which specifically addresses situations where integer arithmetic operations produce results that wrap around to incorrect values. The exploitation of this flaw could enable traffic shaping manipulation attacks where an attacker might cause unexpected bandwidth allocation patterns or potentially create denial-of-service conditions through malformed packet processing. The ATT&CK framework would categorize this under T1059 Command and Scripting Interpreter for execution of malicious network configurations, though the actual attack surface is more subtle and involves manipulating kernel networking parameters rather than direct command execution.
The mitigation approach ensures that negative adjusted lengths are clamped before any link-layer framing adjustments, effectively preventing the integer overflow condition from manifesting in the rate accounting calculations. This solution maintains backward compatibility while ensuring that all packet length calculations behave predictably regardless of the overhead values provided by userspace configuration. The fix essentially prevents the problematic arithmetic transition from occurring in the critical path where rate accounting decisions are made, thereby preserving the integrity of the network traffic control mechanisms that depend on accurate packet size modeling.