CVE-2026-98364 in Linux
Summary
by MITRE • 10/06/2026
In the Linux kernel, the following vulnerability has been resolved:
xfrm: hold net_device reference under RCU in bundle creation
xfrm_bundle_create() and xfrm_create_dummy_bundle() read dst->dev into a local pointer without taking a device reference, then pass it to xfrm_fill_dst(). A concurrent RTM_DELLINK replaces dst->dev via dst_dev_put() and frees the old net_device, causing a use-after-free when xfrm6_fill_dst() later dereferences the stale dev pointer.
BUG: KASAN: slab-use-after-free in xfrm6_fill_dst+0x82c/0x860 (net/ipv6/xfrm6_policy.c:86 netdev_hold()) Read of size 8 at addr ffff8880142fe588 by task exploit/153 Call Trace: xfrm6_fill_dst+0x82c/0x860 xfrm_resolve_and_create_bundle+0x21d4/0x2bd0 xfrm_lookup_with_ifid+0x485/0x1640 ip6_dst_lookup_flow+0x19b/0x1e0 udpv6_sendmsg+0x1443/0x2dd0
Fix this by reading dst->dev via dst_dev_rcu() and keeping the RCU read-side critical section active until xfrm_fill_dst() has taken the required device references.
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Analysis
by VulDB Data Team • 10/06/2026
The Linux kernel networking subsystem contains a race condition vulnerability within the IPsec implementation, specifically affecting the XFRM bundle creation process. This flaw arises from improper handling of network device references during the resolution and bundling of routing entries for IPv6 traffic. The core issue is located in functions such as xfrm_bundle_create() and xfrm_create_dummy_bundle(), which are responsible for constructing destination cache bundles used by IPsec to encrypt or authenticate packets. These functions access the dst->dev field, which points to the underlying network device interface, but they do so without acquiring a proper reference count on that device object. This oversight creates a window of vulnerability where the referenced network device can be deallocated while it is still being accessed by concurrent kernel operations.
The technical root cause involves a classic use-after-free scenario driven by concurrency between route lookup and link deletion events. When xfrm_bundle_create() reads dst->dev into a local pointer, it assumes the net_device structure will remain valid for the duration of its execution. However, if another thread or process triggers an RTM_DELLINK operation to remove a network interface during this window, the kernel calls dst_dev_put(), which decrements the reference count and potentially frees the old net_device memory immediately after releasing any other locks. Because xfrm_bundle_create() did not hold a stable reference via RCU (Read-Copy-Update) mechanisms or standard refcounting at the point of access, it retains a dangling pointer to this now-freed memory region. Subsequently, when the code proceeds to call xfrm_fill_dst(), which in turn invokes functions like xfrm6_fill_dst() for IPv6 traffic, it attempts to dereference this stale pointer. This leads to an invalid memory read operation that triggers kernel panic or data corruption depending on whether the freed memory has been reallocated for other purposes.
The operational impact of this vulnerability is significant as it allows a local user with network access capabilities to trigger a denial-of-service condition against the host system. By crafting specific UDPv6 packets that force the execution path through xfrm_lookup_with_ifid and subsequent bundle creation, an attacker can induce the race condition required to free the net_device structure prematurely. The kernel detects this invalid memory access via KASAN (Kernel Address Sanitizer) instrumentation in debug builds or may experience unpredictable behavior including crashes, data corruption, or system instability in production environments where such checks are not active. This vulnerability effectively undermines the reliability of IPsec connections and can be exploited to destabilize network services running on affected Linux kernels without requiring elevated privileges beyond those needed to send packets through the networking stack.
To mitigate this issue, developers must ensure that any access to dst->dev is protected by appropriate synchronization primitives. The fix involves modifying xfrm_bundle_create() and related functions to read the device pointer using dst_dev_rcu(), which safely accesses the pointer under an RCU read-side critical section. Furthermore, it is essential to maintain this RCU lock until after xfrm_fill_dst() has successfully taken a reference on the network device via netdev_hold(). This ensures that the net_device structure remains valid and cannot be freed while the kernel code is still interacting with its fields. System administrators should apply vendor-provided patches or update their Linux kernels to versions where this race condition in the XFRM subsystem has been resolved, thereby restoring memory safety guarantees for IPsec bundle creation operations.
This vulnerability aligns with CWE-416, Use After Free, as it involves accessing a pointer after its associated memory has been freed due to improper reference counting and concurrency control. In terms of attack patterns, this scenario reflects aspects of the ATT&CK technique T1059, Command and Scripting Interpreter, specifically when considering how local exploitation might lead to further system compromise if combined with other vulnerabilities, although primarily it represents a stability issue exploitable for denial-of-service via memory corruption. The fix emphasizes the importance of adhering to RCU protocols in high-concurrency kernel subsystems like networking, where race conditions between packet processing and interface management are common pitfalls that can lead to severe security and reliability issues if not meticulously managed through proper locking and reference counting strategies.