CVE-2025-38159: Out-of-Bounds Read in Realtek rtw88 Linux Driver (High Impact)

A small, two-byte mistake in a Linux Wi‑Fi driver has quietly become a reminder that even trivial-looking changes in kernel code can carry outsized risk: CVE-2025-38159 is an out‑of‑bounds read in the Realtek rtw88 Wi‑Fi driver that was introduced years ago, affects a broad set of devices powered by Realtek chips, and has been assessed as a high‑impact flaw because it can disclose memory and destabilize systems. System and endpoint managers should treat this as a practical reliability and information‑security issue: update kernels or apply mitigations now if your estate runs the affected modules.

Background / Overview​

The vulnerability sits inside the in‑kernel Realtek driver family known as rtw88, which implements support for a variety of Realtek wireless chips used in laptops, small form factor PCs, and many embedded devices. The bug is straightforward in root cause: a buffer—named para in the driver code—was allocated with an insufficient size (two bytes) while code later treats that buffer as containing an operation code followed by five bytes of payload. In short, the driver reads beyond the end of the buffer.
This error was discovered by static analysis tooling and subsequently fixed in the upstream Linux kernel tree. The CVE identifier for the issue is CVE‑2025‑38159. Upstream maintainers and a number of distributions published advisories and patches; vendors have both backported fixes to stable trees and released updated kernel packages for affected distributions.
At a glance:

• Vulnerability type: Out‑of‑bounds read (CWE‑125)
• Affected component: Linux kernel — drivers/net/wireless/realtek/rtw88 (coex/BT‑Wi‑Fi control path)
• Attack surface: Local (an attacker with local access or ability to run code on the host)
• Privileges required: Low (non‑privileged code can often interact with wireless device control interfaces)
• Impact: Confidentiality (information disclosure) and Availability (crashes / DoS) — the vulnerability has been scored in the high range (CVSS ~7.0–7.1 by several vendors)

The fix consists of correcting the para buffer allocation (making the array six bytes long so it holds the op code plus the five data bytes read by the Bluetooth/Wi‑Fi control function), and the patch has been merged into stable kernel lines and backported by multiple distribution vendors.

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Why a two‑byte mistake matters: technical anatomy​

At its root the problem is simple to explain, and that simplicity is part of why this kind of bug is dangerous: the driver creates an array intended to carry a control opcode and some argument bytes, but allocates only two bytes. Later, it calls a helper function to build a firmware (H2C) packet that expects five bytes of data after the opcode. The helper then dereferences offsets up to data + 4, which triggers an out‑of‑bounds read when the passed buffer is too small.
In pseudo terms the flow looks like:

• Driver builds u8 para[2] (incorrect length).
• Driver calls rtw_fw_bt_wifi_control(rtwdev, para[0], &para[1]).
• rtw_fw_bt_wifi_control(..., u8 *data) reads data[0] through data[4].

Because the code reads five bytes starting at &para[1], the para array needs to be at least six bytes long (1 for the opcode + 5 for data). The fix increases the size to six, preventing reads past the intended buffer.
Why is this problematic in practice?

• An out‑of‑bounds read can disclose adjacent kernel memory contents to userland if the driver surface allows data to flow back to a caller. Leaking kernel memory can expose secrets (keys, addresses, pointers) and can assist other local privilege escalation or code‑reuse attacks.
• Even when direct data leak is not possible, an out‑of‑bounds read may index into unmapped pages or otherwise destabilize memory access patterns and cause kernel warnings, oopses, or full system crashes — producing loss of availability for the system’s networking or for the host as a whole.
• The function affected sits in the Wi‑Fi/BT coexistence codepath; that code is invoked in routine device control operations and therefore may be reachable by unprivileged processes that have routine access to wireless device controls (e.g., through standard network management stacks or userland tooling).

The vulnerability was detected by static analysis (the report references the tool Svace). Static tools often find off‑by‑one or off‑by‑size mistakes that human reviewers miss, and this is a good example: the code compiled and ran, but under some inputs it could read memory it shouldn’t.

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Timeline and fixes (summary)​

• Introduction: The problematic change was introduced in earlier kernel development — vendor and kernel announcements identify the problematic patch chain originating in kernel series around the 5.x line.
• Public disclosure: The issue was catalogued and tracked as CVE‑2025‑38159 and published in early July 2025.
• Upstream fix: The kernel community applied a simple and surgical fix: set the para array size to six instead of two and adjust surrounding code as necessary. The fix was included in later stable kernel releases and in the 6.15.x stable maintenance tree.
• Vendor responses: Major distributions and vendors (Ubuntu, Red Hat, SUSE, Debian family and others) issued advisories and rolled the fix into their kernel packages — often with backports to their supported kernel branches. Enterprise and long‑term support vendors provided errata and package updates that include the change.

Because this is a small, targeted change it was straightforward for vendors to backport to stable kernel versions. However, not every vendor or embedded OEM backports the same way or at the same speed, so administrators must check vendor advisories for their specific kernel image.

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Who and what is affected​

The vulnerability affects devices whose kernel contains the rtw88 Realtek driver with the buggy codepath. Practically that includes:

• Laptops and desktops that use Realtek wireless chipsets supported by rtw88 (multiple RTL8xxx series devices).
• Embedded devices, IoT appliances, and small form factor systems that ship with Realtek Wi‑Fi chips.
• Virtual machines that expose host Wi‑Fi hardware directly (rare) or physical systems in a mixed environment.

Who is not affected:

• Systems that use other Realtek drivers (e.g., legacy rtl8xxxu variants) and those that do not load any rtw88 modules are not affected.
• Pure Windows endpoints are not affected by this Linux kernel‑space issue (except in multi‑boot or device vendor scenarios where Linux is present).
• Cloud Linux instances are affected only if the cloud provider’s image includes an affected kernel and loaded rtw88 driver (many cloud images run hardened or minimal networking stacks without Wi‑Fi drivers).

Impact is most meaningful where local code execution or multi‑user access exists and where wireless functionality is enabled — e.g., laptops used by many users, public kiosks, developer workstations, or servers in lab environments.

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Exploitability and real‑world risk​

From the public technical details and vendor scoring, the vulnerability has these notable characteristics:

• Attack vector is local. An attacker must run code on the affected host or otherwise get the host to execute the specific driver path (e.g., by invoking a userland utility that interacts with the Wi‑Fi device).
• Privilege requirement is low — many vendor assessments mark privileges required as low. That means unprivileged userland processes that can use standard networking APIs may be able to trigger the codepath.
• Attack complexity is low in the sense that the root cause is a simple memory read past a small buffer; it does not require complex timing or race conditions.
• Confidentiality and availability impacts are the highest concerns: leaking kernel memory and causing kernel stability problems (repeated exploitation could crash the host). Integrity impact is low or none, because the issue is a read only.
• Public proof‑of‑concept code: at the time of publication there were no widely circulated, weaponized PoCs for remote exploitation. However, the nature of the bug makes local exploitation plausible and attractive to attackers who already have some foothold on a machine.

In short: this is not an unauthenticated network remote code execution vulnerability, but it is a high‑value local vector for attackers who target systems with Realtek rtw88 drivers loaded. For organizations with multi‑user or untrusted user scenarios (for example, university labs, shared developer machines, or thin clients), this raises the profile of a local‑attacker risk.

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Detection and hunting: how to find vulnerable hosts​

To identify affected systems, administrators should apply the following checks:

• Check running kernel version
• Command (general): run uname -r to see the current kernel release. Your vendor advisory will list kernels that include the fix; kernels older than the stable point noted by your vendor may be vulnerable unless backported.
• Check whether rtw88 modules are loaded
• Command: lsmod | grep rtw88
  Look for module names such as rtw88_core, rtw88_pci, and chipset specific modules like rtw88_8821ce, rtw88_8822be, rtw88_usb, etc.
• Inspect kernel dmesg/syslog for anomalies
• Look for oops, WARN, or stack traces referencing rtw88 or rtw_fw_bt_wifi_control. Crashes or repeated warnings in the coex codepath can indicate attempted exploitation or a misbehaving driver.
• Audit package/kernel versions against vendor advisories
• Compare installed kernel package versions against distribution security advisory lists or your vendor’s fixed package list. Many vendors published specific errata IDs for the backport packages.
• For large fleets, use automated inventory and vulnerability scanners
• Integrate kernel and module checks into configuration management and vulnerability scanning (e.g., use package fingerprints and kernel version baselines). Flag endpoints that both run kernels below the fixed threshold and have an rtw88 module present.

Note: the easiest and most reliable detection path is to check for the presence of the rtw88 module and to ensure the kernel package is at or above the vendor‑patched version. If a system does not have any rtw88 module present (because it uses a different Wi‑Fi chipset, or Wi‑Fi is disabled), the risk is effectively zero for that host.

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Mitigation and remediation options​

The only complete remediation is to install a kernel that contains the upstream fix or an equivalent vendor patch/backport. But there are practical interim mitigations you can apply while scheduling the patch roll‑out.
Primary remediation (recommended)

• Apply vendor/repository kernel updates as supplied by your Linux distribution. That is the preferred, supported path for servers and desktop fleets.
• For systems using vendor kernels (RHEL, SUSE SLES, Ubuntu LTS images), use the vendor’s update tooling to install the patched kernel packages and reboot when appropriate.

Interim mitigations (temporary, use with caution)

• Unload the rtw88 kernel modules at runtime (this will disable affected Realtek Wi‑Fi devices until modules are reloaded or system is rebooted):
• Identify modules: lsmod | grep rtw88
• Remove modules (example): sudo modprobe -r rtw88_core rtw88_pci rtw88_8822be rtw88_usb
  Note: exact module names vary by chip; remove chipset modules first, then the core. Failure to remove dependencies will result in errors.
• Blacklist the rtw88 modules to prevent load across reboots:
• Create a file /etc/modprobe.d/blacklist-rtw88.conf containing lines like:
• blacklist rtw88_core
• blacklist rtw88_pci
• blacklist rtw88_8821ce
• Update initramfs if your distribution loads modules from the initramfs and then reboot.
• Warning: blacklisting will disable Realtek Wi‑Fi functionality permanently until you remove the blacklist and reboot; plan user impact accordingly.
• Disable Bluetooth and/or Wi‑Fi coexif features where feasible on systems where coexistence code is invoked. This reduces exposure by blocking the codepath that was commonly observed as the trigger point. Many desktop network managers and BIOS/UEFI settings allow disabling Bluetooth or wireless hardware.
• Configure host hardening:
• Restrict local code execution for untrusted users (e.g., limit shell access, use containerization or restricted profiles).
• Ensure that unprivileged users do not have access to device nodes for networking that could trigger the driver path (rarely on modern systems, but check /dev nodes and policy).

Operational guidance for using mitigations

• Test mitigation on a small set of targets first to confirm impact on connectivity and services.
• Communicate to users when Wi‑Fi will be disabled on managed endpoints — blacklisting the driver will break wireless connectivity.
• Apply patches as soon as vendor packages are available — mitigations are stopgaps, not long‑term solutions.

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For embedded, OEM, and device vendors​

Many embedded and OEM vendors ship kernels with custom backports and configuration choices. The fix is tiny, but the process for delivering it to end users varies:

• Vendors should include the fix in their next firmware/kernel image and, where possible, provide over‑the‑air updates for consumer devices.
• Where updating the kernel is impractical, vendors may implement a micropatch or driver replacement that corrects the buffer size in their specific builds.
• Device makers should prioritize devices where wireless connectivity is exposed to untrusted users or where devices are used in shared/public contexts.

If you are an OEM shipping devices with Realtek Wi‑Fi, coordinate with your kernel/firmware team to ensure the fix is backported into your maintenance kernel branches and schedule an update for end users. Document the update path in release notes and support pages.

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Operational checklist for sysadmins (practical steps)​

• Inventory
• Enumerate systems with rtw88 loaded and collect kernel versions.
• Assess
• Map those systems to risk categories (public access, multi‑user, privileged workloads).
• Patch
• Apply vendor kernel updates or deploy upstream stable kernels that contain the fix.
• Reboot hosts as required.
• Mitigate (if patching is delayed)
• Temporarily unload and/or blacklist rtw88 modules on high‑risk hosts.
• Disable Bluetooth or Wi‑Fi if feasible.
• Monitor
• Watch for kernel logs referencing rtw88 errors or oopses.
• Scan for anomalous network management activity and privilege escalations.
• Communicate
• Notify affected users when Wi‑Fi will be disabled as part of mitigation.
• Document the remediation plan and confirm post‑patch service health.

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Detection caveats and false positives​

• Some systems may report rtw88 modules present but are not running wireless hardware (module present in initramfs or available but not in use). Confirm active usage by checking ip link output for wireless interfaces (iwconfig, ip a) and by reviewing dmesg for device probe events.
• Blacklisting may not fully prevent a module from being present in certain embedded initramfs configurations; rebuilding the initramfs may be necessary.
• Vendor backports may alter the exact kernel package version numbers; always rely on vendor advisory identifiers rather than upstream commits when assessing patched status in an enterprise distribution.

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Why this matters to WindowsForum readers​

Even though this vulnerability lives in the Linux kernel, Windows enthusiasts should care for several reasons:

• Many Windows users dual‑boot with Linux, run Linux in VMs, or run WSL2 with real hardware passthrough scenarios. Those environments can host vulnerable kernels.
• Tech enthusiasts often manage mixed environments — laptops used for both development and everyday work can be a bridge for attackers if volatile local privilege is exploited under a vulnerable kernel.
• The bug demonstrates that small, low‑visibility driver bugs can produce serious availability issues; the lesson applies to all platform maintainers, including Windows device driver teams.

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Final risk assessment and verdict​

CVE‑2025‑38159 is not a remote, unauthenticated wormable flaw, but it is an important local attack surface vulnerability. Its real danger lies in:

• The ease with which local code can trigger the codepath on machines with Realtek Wi‑Fi chips and rtw88 modules loaded.
• The potential for both information disclosure and repeated exploitation leading to availability loss (crashes and kernel instability).
• The large installed base of Realtek Wi‑Fi hardware in consumer and enterprise devices.

Administrators and users should:

• Treat it as a priority for patching on systems that have rtw88 loaded, especially shared or multi‑user endpoints.
• If immediate patching is infeasible, apply conservative mitigations (module blacklisting or disabling Bluetooth/Wi‑Fi coexistence) on higher‑risk hosts.
• Monitor vendor advisories and kernel package updates for your distribution and apply them promptly.

In short: the fix is small, the remediation path is well known, and the mitigation options are practical — but the window for risk remains open until the patch is widely deployed. Prioritize patching machines with real‑world exposure to untrusted users, and treat this CVE as a reminder to include driver‑level checks in kernel and image security baselines.

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Appendix — Quick commands and notes​

• Check kernel: uname -r
• List rtw88 modules: lsmod | grep rtw88
• Remove modules (example): sudo modprobe -r rtw88_8822be rtw88_pci rtw88_core
  (Adjust module names for your chip. Remove chip modules before core.)
• Blacklist modules (example): create /etc/modprobe.d/blacklist-rtw88.conf with:
• blacklist rtw88_core
• blacklist rtw88_pci
• blacklist rtw88_8821ce
  Then rebuild initramfs if your distribution requires it and reboot.
• Re‑enable: remove blacklist file and reboot or sudo modprobe rtw88_core (if kernel contains the module).

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A small change in a low‑level driver has produced a high‑value lesson: driver code is security‑critical, and even tiny buffer size mistakes can have real consequences. Treat rtw88 CVE‑2025‑38159 as a real operational risk — inventory affected hosts, apply vendor kernel patches, and if necessary use conservative mitigations to protect high‑risk systems until patches are in place.

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Source: MSRC Security Update Guide - Microsoft Security Response Center