Overview
CVE-2025-9558 is a high-severity out-of-bounds (OOB) write vulnerability found in the gen_prov_start function within the pb_adv.c file of the Zephyr Real-Time Operating System (RTOS). This flaw can allow an attacker to potentially overwrite arbitrary memory locations, leading to system crashes, denial of service, or potentially even arbitrary code execution on affected devices.
Technical Details
The vulnerability stems from a lack of input validation within the gen_prov_start function. Specifically, the function copies the full length of received data into the link.rx.buf receiver buffer without checking if the data size exceeds the buffer’s allocated capacity. This unchecked copy operation creates an opportunity for an attacker to send a specially crafted packet larger than the buffer, causing an out-of-bounds write. The code segment directly responsible is within the Bluetooth Low Energy (BLE) provisioning logic within Zephyr.
This vulnerability occurs because no size checks were implemented prior to calling the memory copy function. By providing crafted input with a size exceeding the allocated memory for link.rx.buf, an attacker could overwrite memory outside the bounds of the intended buffer.
CVSS Analysis
The Common Vulnerability Scoring System (CVSS) score for CVE-2025-9558 is 7.6, indicating a HIGH severity vulnerability. The CVSS vector reflects the potential for significant impact:
- Attack Vector: Network (AV:N)
- Attack Complexity: Low (AC:L)
- Privileges Required: None (PR:N)
- User Interaction: None (UI:N)
- Scope: Unchanged (S:U)
- Confidentiality Impact: None (C:N)
- Integrity Impact: High (I:H)
- Availability Impact: High (A:H)
This score highlights the ease of exploitation (low attack complexity, no privileges required, no user interaction) and the potential for severe consequences (high integrity and availability impact).
Possible Impact
Successful exploitation of CVE-2025-9558 can lead to several critical consequences:
- Denial of Service (DoS): Overwriting critical system memory can cause the device to crash or become unresponsive.
- Arbitrary Code Execution: In some scenarios, an attacker may be able to overwrite memory with malicious code, allowing them to execute arbitrary commands on the affected device.
- Data Corruption: Overwriting adjacent memory regions could corrupt sensitive data, leading to unpredictable system behavior.
These impacts are especially concerning in IoT devices where reliability and security are paramount.
Mitigation and Patch Steps
The recommended mitigation is to apply the patch provided by the Zephyr Project. This patch implements proper input validation in the gen_prov_start function to ensure that the received data size does not exceed the buffer’s capacity. Users should upgrade to the latest version of Zephyr RTOS containing the fix. Consult the security advisory for specific patch details and affected versions.
Specifically, the patch will likely involve adding a size check before the memcpy or similar memory copy function to ensure that the size of the data being copied does not exceed the size of the destination buffer (link.rx.buf).
As a temporary workaround, if patching is not immediately feasible, consider implementing network-level filtering to restrict the size of incoming BLE provisioning packets. However, this should not be considered a complete solution and patching remains the priority.
