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Kernel-Rt Security Update — AlmaLinux 8 (ALSA-2026:21745)
ALSA-2026:21745 updates the real-time kernel (kernel-rt) on AlmaLinux 8, fixing a large batch of vulnerabilities including Bluetooth MGMT use-after-free (CVE-2025-39981), an IMA signature-flag clearing flaw (CVE-2025-68183), a firewire-motu DSP-event buffer overflow (CVE-2025-68347), libceph and further 2026 CVEs — aggregate CVSS 7.8. Only servers running the RT kernel are affected: dnf update kernel-rt and reboot.
High
7.8 CVSS
AlmaLinux 8
What this means under a SharedLicense license
Use-after-free and buffer-overflow classes in the RT kernel carry the same escalation potential as the standard kernel — on real-time workloads (latency-sensitive processing nodes), a local user can crash or compromise the whole host.
The kernel-rt packages provide the Real Time Linux Kernel, which enables fine-tuning for systems with extremely high determinism requirements. Security Fix(es): * kernel: Bluetooth: MGMT: Fix possible UAFs (CVE-2025-39981) * kernel: ima: don't clear IMA_DIGSIG flag when setting or removing non-IMA xattr (CVE-2025-68183) * kernel: ALSA: firewire-motu: fix buffer overflow in hwdep read for DSP events (CVE-2025-68347) * kernel: libceph: make decode_pool() more resilient against corrupted osdmaps (CVE-2025-71116) * kernel: Linux kernel: Denial of service and memory corruption in RDMA umad (CVE-2026-23243) * kernel: Linux kernel: Use-after-free in traffic control (act_ct) may lead to denial of service or privilege escalation (CVE-2026-23270) * kernel: netfilter: nf_conntrack_h323: check for zero length in DecodeQ931() (CVE-2026-23455) * kernel: Bluetooth: SCO: Fix use-after-free in sco_recv_frame() due to missing sock_hold (CVE-2026-31408) * kernel: can: raw: fix ro->uniq use-after-free in raw_rcv() (CVE-2026-31532) * kernel: net: sched: act_csum: validate nested VLAN headers (CVE-2026-31684) * kernel: netfilter: ip6t_eui64: reject invalid MAC header for all packets (CVE-2026-31685) * kernel: netfilter: nf_conntrack_helper: pass helper to expect cleanup (CVE-2026-43027) * kernel: Bluetooth: MGMT: validate LTK enc_size on load (CVE-2026-43020) * kernel: HID: wacom: fix out-of-bounds read in wacom_intuos_bt_irq (CVE-2026-43051) * kernel: smb: client: validate the whole DACL before rewriting it in cifsacl (CVE-2026-31709) * kernel: md/bitmap: fix GPF in write_page caused by resize race (CVE-2026-43163) * kernel: netfilter: xt_tcpmss: check remaining length before reading optlen (CVE-2026-43190) * kernel: xfs: fix freemap adjustments when adding xattrs to leaf blocks (CVE-2026-43158) For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.
Frequently Asked Questions
What is ALSA-2026:21745?
It is AlmaLinux's Important-rated erratum for the kernel-rt real-time kernel on AlmaLinux 8, fixing a large set of CVEs including Bluetooth MGMT use-after-frees (CVE-2025-39981), IMA xattr flag handling (CVE-2025-68183), ALSA firewire-motu buffer overflow (CVE-2025-68347) and multiple 2026 kernel CVEs, at aggregate CVSS 7.8.
Am I affected if I run the standard kernel?
No — this erratum is specifically for the kernel-rt packages used where deterministic latency matters. Servers on the standard kernel get the equivalent fixes through the regular kernel errata instead.
How do I apply the fix?
Run dnf update kernel-rt* and reboot into the updated RT kernel; verify with uname -v (RT kernels carry the PREEMPT_RT suffix) and check the version matches the erratum's build.
Which of the fixed flaws are most notable?
The Bluetooth MGMT use-after-frees matter most for servers with Bluetooth controllers, and the IMA flaw affects systems relying on integrity measurement — a crafted xattr operation could clear the IMA_DIGSIG flag and undermine signature enforcement.
References
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