Linux: Concurrent Execution using Shared Resource with Improper Synchronization
CVE-2026-52945 is a high-severity concurrent execution using shared resource with improper synchronization vulnerability in Linux, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions cfdb22762f903d95c36ab91e9fe6167f22fa9f6d, 42bc3f45425b607a5ca7b7aaaab661b54407c8f8, 168ee1549fa24fff2ab924a2ca7b1d85f30e062d as the first without the flaw, so updating Linux to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.24% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update Linux to cfdb22762f903d95c36ab91e9fe6167f22fa9f6d or 42bc3f45425b607a5ca7b7aaaab661b54407c8f8 or 168ee1549fa24fff2ab924a2ca7b1d85f30e062d or e94b369ff82f9bc84f090f271bd78f41c9f6ab2f, whichever matches your release line, or a later version.
- Update Linux Kernel to 5.15.201 or 6.1.164 or 6.6.127 or 6.12.74, whichever matches your release line, or a later version.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 18e65229a328304a7ef59899a30fd34ad73ed56b up to, but not including, cfdb22762f903d95c36ab91e9fe6167f22fa9f6d; fb978675ccfd4a93549e49624127d8332cc61cbf up to, but not including, 42bc3f45425b607a5ca7b7aaaab661b54407c8f8; 8c9e9cd398777fd60ba202211da1110614cb5bc5 up to, but not including, 168ee1549fa24fff2ab924a2ca7b1d85f30e062d; 933466fc50a8e4eb167acbd0d8ec96a078462e9c up to, but not including, e94b369ff82f9bc84f090f271bd78f41c9f6ab2f; aba544ff9ec522e120b1b3d8b32efa4e6d16d4d7; 6.15.3 up to, but not including, 6.16; 5.15.186 up to, but not including, 5.15.201; 6.1.142 up to, but not including, 6.1.164; and 2 more ranges | cfdb22762f903d95c36ab91e9fe6167f22fa9f6d, 42bc3f45425b607a5ca7b7aaaab661b54407c8f8, 168ee1549fa24fff2ab924a2ca7b1d85f30e062d, e94b369ff82f9bc84f090f271bd78f41c9f6ab2f, 6.16, 5.15.201 |
| Linux | Linux Kernel | 5.15.186 up to, but not including, 5.15.201; 6.1.142 up to, but not including, 6.1.164; 6.6.94 up to, but not including, 6.6.127; 6.12.34 up to, but not including, 6.12.74; 6.15.3 up to, but not including, 6.16 | 5.15.201, 6.1.164, 6.6.127, 6.12.74, 6.16 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- NoneNo data is disclosed.
- Integrity
- NoneNothing can be modified.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. Scored by CNA.
Official description
In the Linux kernel, the following vulnerability has been resolved: Revert "wireguard: device: enable threaded NAPI" This reverts commit 933466fc50a8e4eb167acbd0d8ec96a078462e9c which is commit db9ae3b6b43c79b1ba87eea849fd65efa05b4b2e upstream. We have had three independent production user reports in combination with Cilium utilizing WireGuard as encryption underneath that k8s Pod E/W traffic to certain peer nodes fully stalled. The situation appears as follows: - Occurs very rarely but at random times under heavy networking load. - Once the issue triggers the decryption side stops working completely for that WireGuard peer, other peers keep working fine. The stall happens also for newly initiated connections towards that particular WireGuard peer. - Only the decryption side is affected, never the encryption side. - Once it triggers, it never recovers and remains in this state, the CPU/mem on that node looks normal, no leak, busy loop or crash. - bpftrace on the affected system shows that wg_prev_queue_enqueue fails, thus the MAX_QUEUED_PACKETS (1024 skbs!) for the peer's rx_queue is reached. - Also, bpftrace shows that wg_packet_rx_poll for that peer is never called again after reaching this state for that peer. For other peers wg_packet_rx_poll does get called normally. - Commit db9ae3b ("wireguard: device: enable threaded NAPI") switched WireGuard to threaded NAPI by default. The default has not been changed for triggering the issue, neither did CPU hotplugging occur (i.e. 5bd8de2 ("wireguard: queueing: always return valid online CPU in wg_cpumask_choose_online()")). - The issue has been observed with stable kernels of v5.15 as well as v6.1. It was reported to us that v5.10 stable is working fine, and no report on v6.6 stable either (somewhat related discussion in [0] though). - In the WireGuard driver the only material difference between v5.10 stable and v5.15 stable is the switch to threaded NAPI by default. [0] https://lore.kernel.org/netdev/CA+wXwBTT74RErDGAnj98PqS=wvdh8eM1pi4q6tTdExtjnokKqA@mail.gmail.com/ Breakdown of the problem: 1) skbs arriving for decryption are enqueued to the peer->rx_queue in wg_packet_consume_data via wg_queue_enqueue_per_device_and_peer. 2) The latter only moves the skb into the MPSC peer queue if it does not surpass MAX_QUEUED_PACKETS (1024) which is kept track in an atomic counter via wg_prev_queue_enqueue. 3) In case enqueueing was successful, the skb is also queued up in the device queue, round-robin picks a next online CPU, and schedules the decryption worker. 4) The wg_packet_decrypt_worker, once scheduled, picks these up from the queue, decrypts the packets and once done calls into wg_queue_enqueue_per_peer_rx. 5) The latter updates the state to PACKET_STATE_CRYPTED on success and calls napi_schedule on the per peer->napi instance. 6) NAPI then polls via wg_packet_rx_poll. wg_prev_queue_peek checks on the peer->rx_queue. It will wg_prev_queue_dequeue if the queue->peeked skb was not cached yet, or just return the latter otherwise. (wg_prev_queue_drop_peeked later clears the cache.) 7) From an ordering perspective, the peer->rx_queue has skbs in order while the device queue with the per-CPU worker threads from a global ordering PoV can finish the decryption and signal the skb PACKET_STATE_CRYPTED out of order. 8) A situation can be observed that the first packet coming in will be stuck waiting for the decryption worker to be scheduled for a longer time when the system is under pressure. 9) While this is the case, the other CPUs in the meantime finish decryption and call into napi_schedule. 10) Now in wg_packet_rx_poll it picks up the first in-order skb from the peer->rx_queue and sees that its state is still PACKET_STATE_UNCRYPTED. The NAPI poll routine then exits e ---truncated---
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Concurrent Execution using Shared Resource with Improper Synchronization
The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.
How developers prevent this class of flaw
- In languages that support it, use synchronization primitives. Only wrap these around critical code to minimize the impact on performance.
- Use thread-safe capabilities such as the data access abstraction in Spring.
- Minimize the usage of shared resources in order to remove as much complexity as possible from the control flow and to reduce the likelihood of unexpected conditions occurring. Additionally, this will minimize the amount of synchronization necessary and may even help to reduce the likelihood of a denial of service where an attacker may be able to repeatedly trigger a critical section (CWE-400).
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
Recent Concurrent Execution using Shared Resource with Improper Synchronization vulnerabilities
- 9.8 Critical severity
- 7.5 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.1 High severity
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