CVE-2024-44940 in Linux
Summary
by MITRE • 08/26/2024
In the Linux kernel, the following vulnerability has been resolved:
fou: remove warn in gue_gro_receive on unsupported protocol
Drop the WARN_ON_ONCE inn gue_gro_receive if the encapsulated type is not known or does not have a GRO handler.
Such a packet is easily constructed. Syzbot generates them and sets off this warning.
Remove the warning as it is expected and not actionable.
The warning was previously reduced from WARN_ON to WARN_ON_ONCE in commit 270136613bf7 ("fou: Do WARN_ON_ONCE in gue_gro_receive for bad proto callbacks").
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Analysis
by VulDB Data Team • 09/29/2025
The vulnerability identified as CVE-2024-44940 resides within the Linux kernel's forwarding offload unit implementation, specifically affecting the Generic UDP Encapsulation (GUE) Generic Receive Offload (GRO) handling mechanism. This issue manifests in the fou subsystem where the kernel attempts to process encapsulated packets through the gue_gro_receive function. The vulnerability stems from an overly aggressive warning mechanism that triggers when encountering unsupported encapsulation protocols or those lacking proper GRO handlers. The technical flaw represents a design oversight where the kernel's defensive programming includes a warning that is both misleading and non-actionable, as the condition it detects is expected behavior rather than an actual error state.
The operational impact of this vulnerability primarily affects system stability through unnecessary warning messages that can clutter kernel logs and potentially trigger false positive alerts in monitoring systems. When the kernel encounters packets with unknown encapsulation types or protocols without GRO handlers, the previous implementation would generate a WARN_ON_ONCE message, which although not crashing the system, creates noise in system diagnostics and can obscure legitimate warnings. This behavior is particularly problematic in environments where automated monitoring systems rely on kernel log analysis for security incident detection. The vulnerability was initially introduced when a previous commit 270136613bf7 reduced the warning from a hard failure to a warning-only mechanism, but the underlying issue persisted. The warning was generated by syzbot, an automated fuzzer that creates various packet constructs to test kernel robustness, including packets with unsupported protocols that naturally trigger this condition.
The resolution to CVE-2024-44940 involves removing the WARN_ON_ONCE statement from the gue_gro_receive function, acknowledging that encountering unsupported protocols is a normal operational condition rather than an exceptional error requiring warning. This change aligns with proper kernel design principles where expected edge cases should not generate warning messages that confuse administrators and system monitoring tools. The fix addresses the root cause by recognizing that packet processing should gracefully handle unknown encapsulation types without generating alerts, as these conditions are part of normal network traffic variations and protocol evolution. From a cybersecurity perspective, this vulnerability represents a low-severity issue that primarily impacts operational efficiency rather than security posture, though it could potentially be exploited to create log flooding conditions in monitored environments. The mitigation approach follows established kernel development practices where non-actionable warnings are removed to maintain system reliability and reduce false positive alerting that could mask actual security incidents. This change reflects the broader principle of maintaining clean kernel logs and proper error handling that aligns with industry standards for robust system design and operational best practices. The solution is consistent with common security practices outlined in CWE categories related to defensive programming and proper error handling, ensuring that kernel subsystems maintain their intended operational behavior without generating misleading diagnostic information.