Linux: Concurrent Execution using Shared Resource with Improper Synchronization
CVE-2026-63858 is a high-severity concurrent execution using shared resource with improper synchronization vulnerability in Linux, with a CVSS 3.1 base score of 7.8 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, without any action from a user. The record lists versions 768daa9f4276be4007e88dea61a378c8582ba008, 4e69bfb32b2db323d9205fdb30e284481b37817c, 10f79dbd7719d1da9f5884d13060322d8729f091 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 0.1% 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 768daa9f4276be4007e88dea61a378c8582ba008 or 4e69bfb32b2db323d9205fdb30e284481b37817c or 10f79dbd7719d1da9f5884d13060322d8729f091 or 5.11, whichever matches your release line, or a later version.
- Update Linux Kernel to 5.11 or 5.16 or 5.18 or 5.19, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | b6d9014a3335194590abdd2a2471ef5147a67645 up to, but not including, 768daa9f4276be4007e88dea61a378c8582ba008; b6d9014a3335194590abdd2a2471ef5147a67645 up to, but not including, 4e69bfb32b2db323d9205fdb30e284481b37817c; b6d9014a3335194590abdd2a2471ef5147a67645 up to, but not including, 10f79dbd7719d1da9f5884d13060322d8729f091; 7a248f9c74f9f62799718c12efd9e9e391d60b6f; f275989ad04159dbfc62cefb65ba9c5ba1d7c34f; 62d91062058b42bf70b2c3446aec397bb0ce15ee; 99180dec5ae582227219d1fdd0dd5ccf53ec7491; 5.10.122 up to, but not including, 5.11; and 4 more ranges | 768daa9f4276be4007e88dea61a378c8582ba008, 4e69bfb32b2db323d9205fdb30e284481b37817c, 10f79dbd7719d1da9f5884d13060322d8729f091, 5.11, 5.16, 5.18 |
| Linux | Linux Kernel | 5.10.122 up to, but not including, 5.11; 5.15.47 up to, but not including, 5.16; 5.17.15 up to, but not including, 5.18; 5.18.4 up to, but not including, 5.19; 5.19.1 up to, but not including, 6.18.57; 6.19 up to, but not including, 7.0.10; 5.19; 7.1 | 5.11, 5.16, 5.18, 5.19, 6.18.57, 7.0.10 |
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
- LocalThe attacker needs local access or must trick a user into running something.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- LowA basic user account is enough.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by CNA.
Official description
In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_tables: add hook transactions for device deletions Restore the flag that indicates that the hook is going away, ie. NFT_HOOK_REMOVE, but add a new transaction object to track deletion of hooks without altering the basechain/flowtable hook_list during the preparation phase. The existing approach that moves the hook from the basechain/flowtable hook_list to transaction hook_list breaks netlink dump path readers of this RCU-protected list. It should be possible use an array for nft_trans_hook to store the deleted hooks to compact the representation but I am not expecting many hook object, specially now that wildcard support for devices is in place. Note that the nft_trans_chain_hooks() list contains a list of struct nft_trans_hook objects for DELCHAIN and DELFLOWTABLE commands, while this list stores struct nft_hook objects for NEWCHAIN and NEWFLOWTABLE. Note that new commands can be updated to use nft_trans_hook for consistency. This patch also adapts the event notification path to deal with the list of hook transactions.
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: no, technical impact: total).
- 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
- 9.8 Critical severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
Spotted an error? Tell us.