CVE-2026-93234 in Linux
Summary
by MITRE • 09/24/2026
In the Linux kernel, the following vulnerability has been resolved:
drm/gud: validate TV mode names before creating enum property
The GUD protocol returns TV mode names as fixed-size GUD_CONNECTOR_TV_MODE_NAME_LEN entries and requires each name to be NUL-terminated.
gud_connector_add_tv_mode() currently passes each fixed-size entry directly to drm_mode_create_tv_properties_legacy(), which eventually reaches drm_property_add_enum() and strlen(). If a device returns an entry without a terminating NUL byte, strlen() reads past the end of the slot and can run beyond the allocated buffer, triggering an out-of-bounds read.
Validate that each returned TV mode name contains a NUL terminator within its fixed-size slot before passing it to the DRM property code. If a malformed entry is found, reject the device response with -EIO.
This fixes the out-of-bounds read without changing the handling of valid devices, and avoids silently truncating malformed protocol data.
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Analysis
by VulDB Data Team • 09/24/2026
The Linux kernel's Direct Rendering Manager subsystem contains a vulnerability within the GUD driver that allows for an out-of-bounds memory read when processing TV mode names from connected display hardware. This flaw stems from insufficient validation of input data received via the GUD protocol, which is commonly used in USB-based display adapters and docking stations. The specific issue resides in the gud_connector_add_tv_mode function, which is responsible for registering television modes with the DRM subsystem. According to the GUD specification, TV mode names are transmitted as fixed-size entries defined by GUD_CONNECTOR_TV_MODE_NAME_LEN, and each entry must be strictly NUL-terminated to ensure safe string processing downstream.
The technical root cause of this vulnerability lies in the direct pass-through of these fixed-size buffers without verifying their internal structure before they reach lower-level DRM functions. When gud_connector_add_tv_mode invokes drm_mode_create_tv_properties_legacy, which subsequently calls drm_property_add_enum and eventually strlen(), it assumes that the provided buffer contains a valid NUL terminator within its allocated bounds. If a malicious or malfunctioning device returns an entry where the final byte is not zero, the strlen function will continue reading memory beyond the end of the fixed-size slot. This results in an out-of-bounds read operation, potentially exposing kernel memory contents to user space through subsequent property queries or causing a general protection fault if the accessed memory page is unmapped.
From a security classification perspective, this vulnerability aligns with CWE-125, which describes Out-of-Bounds Read vulnerabilities where software reads data past the end of a buffer. In terms of attack vectors and tactics, this flaw can be leveraged in scenarios consistent with ATT&CK technique T1083, File and Directory Discovery, as an attacker controlling or spoofing a USB display device could potentially leak sensitive kernel memory information. Furthermore, depending on the specific system configuration and whether the out-of-bounds read triggers a crash, it may also relate to CWE-400 Uncontrolled Resource Consumption if used for denial of service purposes by inducing repeated faults during mode enumeration.
The operational impact of this vulnerability is significant because it affects systems using GUD-compliant hardware that interact with the Linux kernel's display stack. An attacker with physical access who can plug in a compromised USB-C dock or adapter could exploit this flaw to read arbitrary kernel memory, potentially leaking cryptographic keys, process credentials, or other sensitive data residing near the allocated buffer on the heap or stack. Additionally, if the out-of-bounds read accesses invalid memory pages, it will cause an immediate kernel panic, leading to a denial of service for the entire system without requiring any authentication or prior compromise.
The resolution implemented in this patch introduces explicit validation logic within gud_connector_add_tv_mode before passing data to the DRM property creation functions. The fix checks whether each TV mode name contains a NUL terminator strictly within its fixed-size slot boundaries. If the validator detects that no such terminator exists, it rejects the device response by returning an -EIO error code rather than proceeding with the unsafe operation. This approach ensures that malformed protocol data is discarded safely without altering the behavior for valid devices and prevents silent truncation or memory corruption issues associated with improperly terminated strings.
To mitigate this vulnerability in environments where kernel updates are not immediately available, administrators should exercise caution when connecting unknown or untrusted USB display adapters to production systems. Physical security controls remain critical as the attack vector requires direct hardware connection. However, the most effective mitigation is applying the upstream Linux kernel patch that enforces strict NUL-termination validation for GUD TV mode names. Regularly updating the operating system ensures that these input validation checks are active and prevents exploitation of this out-of-bounds read condition by malicious peripheral devices.