CVE-2026-53082: Linux Kernel 6pack Driver Uninitialized Value Denial of Service

Technical summary

CVE-2026-53082 is an uninitialized value read vulnerability (CWE-908) in the Linux kernel's net/drivers/hamradio/6pack.c driver. The sixpack_receive_buf() function fails to properly handle TTY error flags when processing incoming data. Specifically, the function iterates through a flags buffer (fp[]) to detect error conditions but does not advance the corresponding data pointer (cp), and passes the full byte count—including flagged error bytes—to sixpack_decode(). Since the TTY layer does not guarantee meaningful values at positions marked with error flags, this results in KMSAN (Kernel Memory Sanitizer) reporting uninitiated memory access. The fix involves processing bytes sequentially, advancing the data pointer on each iteration, and filtering out bytes with error flags before passing them to the decoder, aligning the implementation with similar drivers (slip_receive_buf and mkiss_receive_buf).

Business impact

While the CVSS score of 5.5 (Medium) reflects local attack surface and limited scope, the practical impact depends on kernel build configuration and the availability of 6pack device access. Organizations using amateur radio or specialized networking equipment with 6pack protocol support may face system instability or crashes triggered by malformed data on compromised links. For most enterprise environments not deploying 6pack devices, this is a lower-priority issue; however, telecommunications, research, or hobbyist setups using the driver should treat it as a stability concern.

Affected systems

The vulnerability affects the Linux kernel across multiple versions. The affected vendor/product entries reference linux/linux_kernel. To determine which specific kernel versions contain the flaw and which patches resolve it, consult the official Linux kernel security advisories or your distribution's security bulletins. Systems running custom or embedded kernels that include the 6pack driver are at potential risk.

Exploitability

Exploitation requires local access (CVSS AV:L) and does not require elevated privileges (PR:L indicates low privilege), meaning a standard user account with access to a 6pack TTY device can trigger the condition. The attack vector is passive—no user interaction is needed beyond normal device usage. However, 6pack is not widely deployed in modern systems, significantly limiting the practical attack surface. The vulnerability manifests as a kernel memory access violation rather than code execution.

Remediation

Apply the patch that implements sequential byte-by-byte processing with proper error flag handling in sixpack_receive_buf(). This involves advancing the data pointer (cp) on each iteration, checking the error flag (fp[]) for each byte, and filtering out flagged bytes before passing valid data to sixpack_decode(). Verify the specific patch version against your Linux distribution's security advisory or the upstream kernel repository.

Patch guidance

Check your Linux distribution's security advisory or kernel.org for the patched kernel version. The fix must be applied via a kernel update; no userspace workaround is available. If you depend on 6pack functionality, prioritize kernel updates promptly. If 6pack is not in use, this may be part of a routine security update and should be applied on your standard patching schedule. Test kernel updates in a non-production environment first to ensure compatibility with your ham radio or specialized networking equipment.

Detection guidance

Monitor kernel logs (dmesg, journalctl) for KMSAN warnings and uninitialized value reports originating from the 6pack driver code paths (net/drivers/hamradio/6pack.c). System stability monitoring may show unexpected kernel oops or crashes correlated with 6pack device activity. Check running kernel version (uname -r) and compare against your distribution's patched versions. If 6pack is not required, consider disabling the module (modprobe -r sp0, or adding blacklist entries to modprobe configuration) to eliminate the attack surface entirely.

Why prioritize this

Although the CVSS score is Medium (5.5) and the vulnerability is not yet on the KEV catalog, prioritization should be driven by actual 6pack deployment in your environment. Local-only attack surface and lack of code execution capability reduce urgency for general enterprise deployments. However, organizations operating amateur radio networks, telecommunications research labs, or specialized packet radio systems should prioritize this patch to prevent unexpected kernel crashes during critical operations. For typical enterprise environments without 6pack hardware, this is a lower-priority routine update.

Risk score, explained

The CVSS v3.1 score of 5.5 (Medium) reflects: local attack vector (AV:L), low complexity (AC:L), low privilege requirement (PR:L), no user interaction (UI:N), unchanged scope (S:U), no confidentiality impact (C:N), no integrity impact (I:N), and high availability impact (A:H). The score appropriately captures denial-of-service risk via kernel crash without the potential for data breach or privilege escalation. The medium severity is justified by the narrow attack surface (6pack driver) and privilege/access requirements, balanced against the high impact when triggered.

Frequently asked questions