CVE-2026-11809 in Zephyr
Summary
by MITRE • 08/11/2026
The UpdateHub OTA client in subsys/mgmt/updatehub/updatehub.c contains an out-of-bounds / uninitialized-memory read in z_impl_updatehub_probe(). The probe response from the UpdateHub server is copied into a heap buffer (metadata) that is correctly NUL-terminated, but a second buffer (metadata_copy) is allocated with k_malloc (unzeroed) and filled with memcpy(metadata_copy, metadata, strlen(metadata)), which omits the terminating NUL. Everything after the copied content remains uninitialized heap.
When the first json_obj_parse() over the array descriptor fails, the code falls back to json_obj_parse(metadata_copy, strlen(metadata_copy), ...). The strlen() call scans past the copied bytes through uninitialized heap and, if no zero byte is found before the end of the allocation, reads beyond the buffer; the resulting over-long length is then parsed as JSON. The probe payload is fully controlled by the (malicious, compromised, or — without the optional CONFIG_UPDATEHUB_DTLS — on-path) UpdateHub server, which can craft a large payload that fails the first parse to drive this path.
The consequence is a read of uninitialized heap, with a worst case of an out-of-bounds read past the metadata_copy allocation that can fault and crash the update thread/device, producing a network-triggerable denial of service. The over-read data is consumed only internally to evaluate the update and is not returned to the attacker, so there is no direct information disclosure and no out-of-bounds write.
The fix zeroes metadata_copy with memset before the copy, guaranteeing NUL termination and bounding strlen() within the allocation.
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Analysis
by VulDB Data Team • 08/11/2026
The vulnerability exists within the UpdateHub over-the-air client implementation in the subsys/mgmt/updatehub/updatehub.c file where an out-of-bounds memory read occurs in the z_impl_updatehub_probe() function. This flaw stems from improper handling of heap-allocated buffers during JSON parsing operations, creating a potential denial of service condition that can be triggered remotely through malicious probe responses.
The technical implementation involves two distinct buffer allocations where the first buffer metadata is correctly NUL-terminated upon copying from the server response. However, a second buffer metadata_copy is allocated using k_malloc which does not initialize memory contents, leading to uninitialized heap data being copied into this buffer. The memcpy operation copies exactly strlen(metadata) bytes without including the terminating NUL character, leaving subsequent heap memory uninitialized and potentially containing arbitrary data.
When the initial json_obj_parse() operation fails while processing the array descriptor, the code executes a fallback mechanism that processes the metadata_copy buffer using json_obj_parse(metadata_copy, strlen(metadata_copy), ...). The critical flaw occurs because strlen(metadata_copy) scans through the uninitialized heap memory beyond the intended copied content, potentially reading hundreds or thousands of bytes until it encounters a zero byte. This over-long length parameter is then passed to the JSON parser, causing it to process uninitialized memory as structured data.
This vulnerability aligns with CWE-125 Out-of-Bounds Read and CWE-787 Out-of-Bounds Write patterns, though the specific implementation results in read-only issues rather than write operations. The attack surface maps to ATT&CK technique T1059 Command and Scripting Interpreter for executing malicious payloads that can trigger the problematic code path through crafted server responses.
The operational impact represents a network-triggerable denial of service condition where a malicious or compromised UpdateHub server can craft probe responses designed to force execution of the fallback parsing logic. The device thread crashes when attempting to parse the over-read data, resulting in complete system unavailability. The vulnerability affects devices without optional CONFIG_UPDATEHUB_DTLS protection, making them susceptible to on-path attacks where attackers can intercept and modify communications.
The fix implements proper memory initialization by zeroing the metadata_copy buffer with memset before copying the metadata content, ensuring guaranteed NUL termination and bounding strlen() operations within the allocated memory boundaries. This mitigation prevents the scanning of uninitialized heap data while maintaining all existing functionality and security properties. The solution addresses the root cause rather than merely patching symptoms, providing robust protection against similar classes of vulnerabilities in future implementations.
The exploitability of this vulnerability requires an attacker to either compromise the UpdateHub server directly or position themselves on-path to modify communications, making it particularly concerning for IoT deployments where network security controls may be insufficient. The lack of information disclosure means the over-read data cannot be exfiltrated, but the crash condition provides sufficient impact for denial of service attacks that can be executed remotely with minimal privileges required.