CVE-2023-0266
Linux Kernel Use-After-Free Vulnerability
Description
CVE-2023-0266 is a high-severity use-after-free vulnerability in the ALSA PCM package of the Linux Kernel. The flaw arises from missing locks in the SNDRV_CTL_IOCTL_ELEM_READ and SNDRV_CTL_IOCTL_ELEM_WRITE32 ioctl handlers, which can be exploited to achieve privilege escalation from a system user to ring0 (kernel) access. CVE-2023-0266 affects the Linux Kernel and Debian Linux distributions, and CISA has confirmed active exploitation by adding it to the Known Exploited Vulnerabilities catalog. Organizations running affected Linux systems should apply the recommended kernel patches immediately to mitigate this use-after-free vulnerability.
KEV Information
CVSS Score
CVSS:3.1/AV:A/AC:H/PR:L/UI:N/S:C/C:L/I:H/A:HOpen in CalculatorAffected Products
| Vendor | Product | Version |
|---|---|---|
| debian | debian linux | 10.0 |
| linux | linux kernel | >= 4.14, < 4.14.303; >= 4.15, < 4.19.270; >= 4.20, < 5.4.229; >= 5.5, < 5.10.163; >= 5.11, < 5.15.88; >= 5.16, < 6.1.6 |
Multiple CVSS Assessments
CVSS:3.1/AV:A/AC:H/PR:L/UI:N/S:C/C:L/I:H/A:H
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
References
- https://git.kernel.org/pub/scm/linux/kernel/git/stable/stable-queue.git/tree/queue-5.10/alsa-pcm-move-rwsem-lock-inside-snd_ctl_elem_read-to-prevent-uaf.patch?id=72783cf35e6c55bca84c4bb7b776c58152856fd4(Mailing List, Patch, Vendor Advisory)
- https://github.com/torvalds/linux/commit/56b88b50565cd8b946a2d00b0c83927b7ebb055e(Patch)
- https://github.com/torvalds/linux/commit/becf9e5d553c2389d857a3c178ce80fdb34a02e1(Patch)
- https://lists.debian.org/debian-lts-announce/2023/05/msg00006.html(Mailing List, Third Party Advisory)
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2023-0266(US Government Resource)
Weakness Type
CWE-416: Use After Free
The use-after-free weakness in CVE-2023-0266 occurs within the Linux Kernel's ALSA (Advanced Linux Sound Architecture) subsystem, where missing synchronization locks allow a race condition that references memory after it has been freed. This enables an attacker with system-level access to manipulate freed memory in the PCM control path, ultimately escalating privileges to kernel-level execution.
Learn more: CWE-416 — Use After Free
Impact Analysis
CVE-2023-0266 carries a CVSS v3.1 score of 7.9 (High), reflecting the severity of a kernel-level privilege escalation vulnerability in the Linux operating system. Attack Vector (Adjacent Network): The vulnerability requires the attacker to be on the same network segment or adjacent network as the target, limiting remote exploitation to local network scenarios. Attack Complexity (High): Exploitation requires precise timing to trigger the race condition caused by missing locks, making successful exploitation more difficult. Privileges Required (Low): A system-level user account is needed to interact with the ALSA ioctl interface. User Interaction (None): No action from another user is required for the attack to succeed. Scope (Changed): The vulnerability can affect resources beyond the vulnerable component, as kernel-level access provides control over the entire system. Integrity and Availability (both High): Successful exploitation allows arbitrary kernel code execution and can lead to complete system compromise, while Confidentiality (Low) indicates limited initial data exposure before full escalation.
Exploit Maturity
CISA has confirmed active exploitation of CVE-2023-0266 in the wild by adding it to the Known Exploited Vulnerabilities catalog, with a remediation deadline of April 20, 2023. No publicly available exploit code or proof-of-concept has been identified in the reference materials, though kernel patches and commit references are available. The EPSS score of 0.08% (24th percentile) is relatively low, suggesting that while active exploitation has been observed, it has not been widespread, likely due to the high attack complexity and adjacent-network access requirements.
Remediation
- Apply the Linux Kernel patch immediately. As directed by CISA, apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable. Upgrade the Linux Kernel past commit 56b88b50565cd8b946a2d00b0c83927b7ebb055e, which adds the necessary locking to the ALSA PCM control path.
- Update Debian-based distributions by applying the security update referenced in the Debian LTS announcement (debian-lts-announce/2023/05/msg00006), which backports the fix for CVE-2023-0266 to supported kernel versions.
- Restrict access to ALSA ioctl interfaces by limiting which users and processes can interact with sound device control nodes, reducing the attack surface for the use-after-free vulnerability. Consider disabling unnecessary sound subsystem access on servers and headless systems.
- Monitor kernel logs for signs of unexpected ALSA subsystem behavior, kernel panics, or privilege escalation attempts that could indicate exploitation of CVE-2023-0266. Review audit logs for unusual ioctl calls to sound device control interfaces.
- Enable kernel security hardening features such as KASLR, SMEP, and SMAP to make exploitation of use-after-free vulnerabilities more difficult, and consider deploying kernel live-patching solutions to minimize downtime during remediation.
Technical Details
CVE-2023-0266 is a use-after-free vulnerability (CWE-416) in the Linux Kernel's ALSA PCM subsystem, specifically in the SNDRV_CTL_IOCTL_ELEM_READ and SNDRV_CTL_IOCTL_ELEM_WRITE32 ioctl handlers. The root cause is missing read/write semaphore locks that should protect concurrent access to control element data structures; without these locks, a race condition allows one thread to free memory while another thread still holds a reference to it. The CVSS vector (AV:A/AC:H/PR:L/UI:N/S:C/C:L/I:H/A:H) reflects that the attack requires adjacent network access and high complexity due to the race condition timing, but the changed scope indicates that successful exploitation breaks out of the ALSA subsystem boundary to gain ring0 kernel access. The fix, implemented in kernel commit 56b88b50565cd8b946a2d00b0c83927b7ebb055e, moves the rwsem lock inside the snd_ctl_elem_read function to properly serialize access and prevent the use-after-free condition.
Frequently Asked Questions
Is CVE-2023-0266 being actively exploited?
Yes, CVE-2023-0266 has been confirmed as actively exploited in the wild. CISA added it to the Known Exploited Vulnerabilities catalog with a remediation deadline of April 20, 2023. There is no known association with ransomware campaigns at this time.
What products are affected by CVE-2023-0266?
CVE-2023-0266 affects the Linux Kernel's ALSA PCM package and Debian Linux distributions. The vulnerability exists in kernel versions prior to the fix in commit 56b88b50565cd8b946a2d00b0c83927b7ebb055e, impacting any system running an unpatched Linux Kernel with the ALSA sound subsystem enabled.
How do I fix CVE-2023-0266?
Upgrade your Linux Kernel to a version that includes commit 56b88b50565cd8b946a2d00b0c83927b7ebb055e or later. For Debian-based systems, apply the security update from the Debian LTS announcement. Additionally, restrict access to ALSA ioctl interfaces on systems where sound functionality is not required.
How severe is CVE-2023-0266?
CVE-2023-0266 has a CVSS v3.1 score of 7.9 (High severity). While the EPSS percentile of 24.3% suggests relatively limited exploitation probability, the confirmed active exploitation by CISA and the potential for kernel-level privilege escalation make this a high-priority vulnerability for remediation.
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