CVE-2026-22987 in Linux
Summary
by MITRE • 01/23/2026
In the Linux kernel, the following vulnerability has been resolved:
net/sched: act_api: avoid dereferencing ERR_PTR in tcf_idrinfo_destroy
syzbot reported a crash in tc_act_in_hw() during netns teardown where tcf_idrinfo_destroy() passed an ERR_PTR(-EBUSY) value as a tc_action pointer, leading to an invalid dereference.
Guard against ERR_PTR entries when iterating the action IDR so teardown does not call tc_act_in_hw() on an error pointer.
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Analysis
by VulDB Data Team • 05/18/2026
The vulnerability identified as CVE-2026-22987 represents a critical NULL pointer dereference flaw within the Linux kernel's traffic control subsystem, specifically affecting the net/sched module responsible for packet classification and action execution. This issue manifests during network namespace teardown operations when the kernel attempts to clean up traffic control actions, creating a scenario where error pointers are improperly handled as valid action objects. The vulnerability was discovered through automated fuzzing analysis by syzbot, which identified a crash pattern in the tc_act_in_hw() function during cleanup phases, indicating a fundamental flaw in how error conditions are managed within the kernel's internal data structures.
The technical root cause resides in the tcf_idrinfo_destroy() function which processes the Internal Data Representation (IDR) structure containing traffic control actions. When network namespace teardown occurs, this function receives an ERR_PTR(-EBUSY) value that represents an error condition rather than a valid tc_action pointer. The kernel's iteration logic fails to properly distinguish between valid action pointers and error pointers, leading to a situation where tc_act_in_hw() is invoked on what appears to be a valid pointer but is actually an error indicator. This violates fundamental kernel programming practices and creates a path for invalid memory dereferencing that can result in system crashes or potential privilege escalation scenarios. The flaw aligns with CWE-476 which addresses NULL pointer dereference vulnerabilities, and specifically demonstrates improper error handling in kernel data structures.
The operational impact of this vulnerability extends beyond simple system crashes to potentially compromise system stability and security during normal network operations. During network namespace cleanup, which occurs when network interfaces are removed or when containers are terminated, the kernel's traffic control subsystem may encounter this condition, leading to unpredictable behavior and system instability. The vulnerability affects systems running Linux kernels that implement the traffic control framework, particularly those utilizing network namespaces for containerization or virtualization environments where frequent namespace creation and destruction occurs. Attackers could potentially exploit this condition to cause denial of service attacks or, in more sophisticated scenarios, leverage the memory corruption to execute arbitrary code with kernel privileges, representing a significant threat to system integrity and availability.
Mitigation strategies for CVE-2026-22987 require immediate kernel updates from vendors that have patched this specific vulnerability, as the fix involves modifying the tcf_idrinfo_destroy() function to properly check for error pointers before attempting to invoke tc_act_in_hw(). The recommended approach involves implementing proper error pointer validation within the IDR iteration logic, ensuring that ERR_PTR values are filtered out before action processing occurs. System administrators should prioritize patching affected kernel versions, particularly those running containerized environments or systems with frequent network namespace operations. Additionally, monitoring for crash patterns related to traffic control subsystem during namespace teardown operations can help identify systems that may be vulnerable. The fix should be accompanied by comprehensive testing in production environments to ensure that legitimate error conditions are properly handled while maintaining the integrity of the traffic control functionality. Organizations using Linux-based systems for networking or containerization should also consider implementing additional monitoring and alerting for kernel crash events related to network subsystem operations.