Linux: Concurrent Execution using Shared Resource with Improper Synchronization
CVE-2026-63883 is a high-severity concurrent execution using shared resource with improper synchronization vulnerability in Linux, with a CVSS 3.1 base score of 7.3 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 c91ea13375f70f6271a0183445e34e83b8f4d8f7, b1159dce10b38eb795e4c96cdc4d34b83cec81c5, 654f45a8569f3cd6ff20bd724a18e0cce65893ba 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 0.13% 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 c91ea13375f70f6271a0183445e34e83b8f4d8f7 or b1159dce10b38eb795e4c96cdc4d34b83cec81c5 or 654f45a8569f3cd6ff20bd724a18e0cce65893ba or 0d2c41a8b00934ddf8a7c1b4cf72dffa1e629c46, whichever matches your release line, or a later version.
- Update Linux Kernel to 6.6.143 or 6.12.93 or 6.18.35 or 7.0.12, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 2aaa43c7077833301c237684cd7bc9ae5e3dec95 up to, but not including, c91ea13375f70f6271a0183445e34e83b8f4d8f7; 2aaa43c7077833301c237684cd7bc9ae5e3dec95 up to, but not including, b1159dce10b38eb795e4c96cdc4d34b83cec81c5; 2aaa43c7077833301c237684cd7bc9ae5e3dec95 up to, but not including, 654f45a8569f3cd6ff20bd724a18e0cce65893ba; 2aaa43c7077833301c237684cd7bc9ae5e3dec95 up to, but not including, 0d2c41a8b00934ddf8a7c1b4cf72dffa1e629c46; 2aaa43c7077833301c237684cd7bc9ae5e3dec95 up to, but not including, 452d6fa37ae9b021f4f6d397dbae077f7296f6f4; 6.3 | c91ea13375f70f6271a0183445e34e83b8f4d8f7, b1159dce10b38eb795e4c96cdc4d34b83cec81c5, 654f45a8569f3cd6ff20bd724a18e0cce65893ba, 0d2c41a8b00934ddf8a7c1b4cf72dffa1e629c46, 452d6fa37ae9b021f4f6d397dbae077f7296f6f4 |
| Linux | Linux Kernel | 6.3 up to, but not including, 6.6.143; 6.7 up to, but not including, 6.12.93; 6.13 up to, but not including, 6.18.35; 6.19 up to, but not including, 7.0.12; 7.1 | 6.6.143, 6.12.93, 6.18.35, 7.0.12 |
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
- LowPerformance or availability is reduced.
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:L. Scored by CNA.
Official description
In the Linux kernel, the following vulnerability has been resolved: serial: qcom_geni: fix kfifo underflow when flush precedes DMA completion IRQ When uart_flush_buffer() runs before the DMA completion IRQ is delivered, the following race can occur (all steps serialized by uart_port_lock): 1. DMA starts: tx_remaining = N, kfifo contains N bytes 2. DMA completes in hardware; IRQ is pending but not yet delivered 3. uart_flush_buffer() acquires the port lock and calls kfifo_reset(), making kfifo_len() = 0 while tx_remaining remains N 4. uart_flush_buffer() releases the port lock 5. DMA IRQ fires; handle_tx_dma() acquires the port lock and calls uart_xmit_advance(uport, tx_remaining) on an empty kfifo uart_xmit_advance() increments kfifo->out by tx_remaining. Since kfifo_reset() already set both in and out to 0, out wraps past in, causing kfifo_len() to return UART_XMIT_SIZE - tx_remaining. The next start_tx_dma() call then submits a DMA transfer of stale buffer data. Fix this by snapshotting kfifo_len() at the start of handle_tx_dma() and skipping uart_xmit_advance() when fifo_len < tx_remaining, which indicates the kfifo was reset by a preceding flush.
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.
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- git.kernel.org/stable/c/0d2c41a8b00934ddf8a7c1b4cf72dffa1e629c46
- git.kernel.org/stable/c/452d6fa37ae9b021f4f6d397dbae077f7296f6f4
- git.kernel.org/stable/c/654f45a8569f3cd6ff20bd724a18e0cce65893ba
- git.kernel.org/stable/c/b1159dce10b38eb795e4c96cdc4d34b83cec81c5
- git.kernel.org/stable/c/c91ea13375f70f6271a0183445e34e83b8f4d8f7
Recent Concurrent Execution using Shared Resource with Improper Synchronization vulnerabilities
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