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Inadequate bounds check and potential underflow in _ux_host_class_hid_report_descriptor_get()

Low
mrybczyn published GHSA-8m9v-jvjp-gmxq Oct 17, 2025

Package

USBX (Eclipse ThreadX)

Affected versions

<= 6.4.2

Patched versions

6.4.3

Description

The _ux_host_class_hid_report_descriptor_get() retrieves and parses a HID report descriptor from a USB HID device. It iteratively calls _ux_host_class_hid_report_item_analyse() to parse individual HID items, adjusting the descriptor pointer and remaining length as it goes.

A serious vulnerability exists in how this loop handles memory bounds:

  1. Insufficient bounds check:

The check:

            if (length < item.ux_host_class_hid_item_report_length)

verifies only one part of the read (the report_length), but not the full read length:

            descriptor += item.ux_host_class_hid_item_report_format;
            descriptor += item.ux_host_class_hid_item_report_length;
  1. Integer underflow:

The line:

length -= (ULONG)(item.ux_host_class_hid_item_report_length + item.ux_host_class_hid_item_report_format);

assumes length is always greater than or equal to the total consumed size. If that’s not the case (e.g., length is 1, but the item reports a size of 16), length underflows and becomes a very large unsigned integer. The loop then continues indefinitely with a corrupted descriptor pointer, leading to out-of-bounds memory reads. This is possible because the length bounds check (see above [and below]) doesn't account for item.ux_host_class_hid_item_report_format

code:

UINT  _ux_host_class_hid_report_descriptor_get(UX_HOST_CLASS_HID *hid, ULONG length)

{

...

    descriptor =  _ux_utility_memory_allocate(UX_SAFE_ALIGN, UX_CACHE_SAFE_MEMORY, length);

...

    transfer_request -> ux_transfer_request_data_pointer =      descriptor;

    transfer_request -> ux_transfer_request_requested_length =  length;

    transfer_request -> ux_transfer_request_function =          UX_GET_DESCRIPTOR;

    transfer_request -> ux_transfer_request_type =              UX_REQUEST_IN | UX_REQUEST_TYPE_STANDARD | UX_REQUEST_TARGET_INTERFACE;

...

    status =  _ux_host_stack_transfer_request(transfer_request);

...

        /* Parse the report descriptor and build the report items.  */

        while (length)

        {

...

            _ux_host_class_hid_report_item_analyse(descriptor, &item);

...

            descriptor +=  item.ux_host_class_hid_item_report_format;

...

            descriptor +=  item.ux_host_class_hid_item_report_length;

       

            /* Verify that the report descriptor is not corrupted.  */

            if (length < item.ux_host_class_hid_item_report_length) <-- this bounds check is insufficient

            {

 

                /* Return error status.  */

                status = (UX_DESCRIPTOR_CORRUPTED);

                break;

            }

 

            /* Adjust the length.  */

            length -=  (ULONG)(item.ux_host_class_hid_item_report_length + item.ux_host_class_hid_item_report_format); <-- length can underflow, at which point this loop goes off the rails

        }

...

}

#define UX_HOST_CLASS_HID_ITEM_TAG_LONG                         0xf0

UINT  _ux_host_class_hid_report_item_analyse(UCHAR *descriptor, UX_HOST_CLASS_HID_ITEM *item)

{

UCHAR       item_byte;

    /* Get the first byte from the descriptor.  */

    item_byte =  *descriptor;

....

    if ((item_byte & UX_HOST_CLASS_HID_ITEM_TAG_MASK) == UX_HOST_CLASS_HID_ITEM_TAG_LONG)

    {

        /* We have a long item, mark its format.  */

        item -> ux_host_class_hid_item_report_format =  UX_HOST_CLASS_HID_ITEM_TAG_LONG;

 

        /* Set the type.  */

        item -> ux_host_class_hid_item_report_type =  (item_byte >> 2) & 3;

 

        /* Get its length (byte 1).  */

        item -> ux_host_class_hid_item_report_length =  (USHORT) *(descriptor + 1);

 

        /* Then the tag (byte 2).  */

        item -> ux_host_class_hid_item_report_tag =  *(descriptor + 2);

    }

...

    return(UX_SUCCESS);

}

Severity

Low

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Local
Attack Complexity High
Attack Requirements None
Privileges Required None
User interaction None
Vulnerable System Impact Metrics
Confidentiality Low
Integrity Low
Availability None
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:L/AC:H/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N

CVE ID

CVE-2025-55096

Weaknesses

Integer Underflow (Wrap or Wraparound)

The product subtracts one value from another, such that the result is less than the minimum allowable integer value, which produces a value that is not equal to the correct result. Learn more on MITRE.