CVE-2026-74693 in Linux
Summary
by MITRE • 08/22/2026
In the Linux kernel, the following vulnerability has been resolved:
net: prestera: validate firmware header length
prestera_fw_hdr_parse() reads the firmware header before checking that the firmware image contains that header.
Reject images shorter than struct prestera_fw_header before decoding the magic and version fields.
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Analysis
by VulDB Data Team • 08/22/2026
The Linux kernel networking subsystem for PrestaEra switches contained a critical logic error in its firmware parsing routine, specifically within the prestera_fw_hdr_parse function. This vulnerability arises from an incorrect order of operations during the validation of incoming firmware images. The driver was designed to parse binary data representing switch firmware, which includes specific structural headers containing metadata such as magic numbers and version identifiers. However, the implementation failed to perform a bounds check on the total size of the provided image before attempting to access fields within that header structure. This oversight creates a scenario where an attacker or malicious actor could supply a truncated or artificially small binary blob intended for firmware update processes.
When the system receives such a malformed input, the function proceeds directly to decode and read specific members of the prestera_fw_header struct without first verifying that the memory buffer is large enough to contain even the minimum size of that structure. This constitutes an out-of-bounds read vulnerability because the code attempts to access memory addresses beyond the end of the allocated or provided data segment. In C programming, accessing memory outside the bounds of a defined array or buffer leads to undefined behavior. Depending on how this specific function is integrated into the broader kernel execution flow and what data resides immediately after the truncated input in memory, this could result in reading garbage values, causing logic errors in subsequent firmware validation steps, or potentially leaking sensitive kernel memory contents if those adjacent bytes contain confidential information.
From a technical classification perspective, this flaw aligns with CWE-125, which describes Out-of-bounds Read vulnerabilities. The root cause is a failure to validate input length prior to processing, violating the principle of defensive programming where all external inputs must be assumed hostile until proven valid by strict size and format checks. In terms of attack vectors, if this firmware parsing routine is accessible via network interfaces or local device management tools that allow users to upload new firmware images, it could potentially be exploited remotely or locally depending on privilege requirements. The ATT&CK framework would categorize the potential impact under techniques related to Discovery, specifically T1082 System Information Discovery, as an out-of-bounds read can inadvertently expose kernel memory contents to the attacker if the returned values are subsequently logged or displayed.
The operational impact of this vulnerability is primarily centered on system stability and information disclosure. While a simple out-of-bounds read may not immediately lead to arbitrary code execution without further exploitation steps involving heap spraying or specific memory layouts, it compromises the integrity of the firmware loading process. A corrupted header interpretation could cause the switch driver to reject valid updates incorrectly or accept invalid ones that might crash the network stack later during runtime. Furthermore, in a multi-tenant environment where kernel stability is paramount, such crashes can lead to denial-of-service conditions affecting all connected services relying on those switches. The lack of proper validation also undermines the security boundary between user-space applications and kernel-space drivers, allowing unprivileged users potentially to probe internal memory states through error responses or side-channel effects if the vulnerability is chained with other flaws.
To mitigate this risk, the primary remediation involves enforcing strict input length verification at the earliest possible stage in the parsing pipeline. Developers must ensure that any binary structure read from external sources has its size validated against sizeof(struct prestera_fw_header) before attempting to dereference pointers or access struct members. This defensive coding practice ensures that the kernel does not attempt to interpret data structures that do not physically exist within the provided buffer. Additionally, implementing comprehensive fuzzing tests for firmware parsers can help identify similar edge cases where length checks are missing in other parts of the networking subsystem. System administrators should apply the latest kernel patches that include this fix immediately to close the gap between unvalidated input and sensitive memory access operations. Regular auditing of driver code against CWE-125 patterns is recommended to prevent recurrence of such logic errors across different network device drivers within the Linux ecosystem.