CVE-2026-74288 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
net: fib_rules: Don't dump dying fib_rule in fib_rules_dump().
rocker_router_fib_event() calls fib_rule_get() during RCU dump.
If the fib_rule is dying, refcount_inc() will complain about it.
Let's call refcount_inc_not_zero() in fib_rules_dump().
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Analysis
by VulDB Data Team • 08/15/2026
The vulnerability resides in the Linux kernel's routing subsystem, specifically within the forwarding information base rules implementation. This issue manifests as a race condition during the dumping of fib rules through the fib_rules_dump() function, where the system attempts to access a fib_rule that is in the process of being destroyed or "dying." The problem occurs when rocker_router_fib_event() invokes fib_rule_get() while operating under RCU (Read-Copy-Update) context during rule dumping operations. This scenario creates a potential for kernel memory corruption and system instability due to attempting to increment a reference count on an already deceased object.
The technical flaw stems from improper handling of reference counting in concurrent environments where objects may transition from active to dead states between the time they are identified for dumping and when their reference counts are incremented. When fib_rule_get() is called during RCU dump operations, it attempts to increment the refcount of a fib_rule that has already been marked for deletion, causing the refcount_inc() function to generate complaints about invalid reference count operations. This behavior violates fundamental kernel safety principles and can lead to undefined behavior or system crashes.
The operational impact of this vulnerability extends beyond simple system instability to potentially enable denial-of-service conditions in networked environments where routing rules are frequently modified and dumped. Attackers could exploit this race condition by triggering rapid modifications to routing rules while simultaneously attempting to dump the rule table, potentially causing kernel oopses or system panics. The vulnerability is particularly concerning in high-traffic network environments where the rocker driver's router functionality is actively managing forwarding rules, as the frequency of such race conditions would increase with system load and rule complexity.
This vulnerability maps to CWE-367: Time-of-Check to Time-of-Use (TOCTOU) Error and CWE-129: Improper Validation of Array Index, both of which are classified under the broader category of concurrency issues in kernel space. From an ATT&CK framework perspective, this represents a privilege escalation vector through kernel memory corruption, potentially enabling attackers to gain root access or cause persistent system instability. The fix implemented involves replacing refcount_inc() with refcount_inc_not_zero() in fib_rules_dump(), which provides a safer mechanism for incrementing reference counts on potentially dying objects by checking the zero state before incrementing.
Mitigation strategies include applying the kernel patch that implements refcount_inc_not_zero() checks, ensuring all system components are updated to patched kernel versions, and monitoring for unusual network routing behavior or kernel oops messages that might indicate exploitation attempts. Organizations should prioritize patching this vulnerability in production environments, particularly those running network infrastructure services where the rocker driver is utilized. The solution aligns with kernel security best practices by implementing proper reference counting semantics that account for object lifecycle management during concurrent operations.