Description

The UpdateHub management subsystem (subsys/mgmt/updatehub/updatehub.c) drives every update operation through a single file-scope ctx structure that holds the CoAP block context, payload buffer, status code, socket, and a one-element poll-fd array fds[1]. Access to ctx was not serialized, and prepare_fds() wrote ctx.fds[ctx.nfds] and incremented ctx.nfds with no bounds check. Two independent paths mutate ctx concurrently: the background autohandler running on the system workqueue, and user-triggered operations reached through the updatehub run shell command, direct API calls, or — since the operations are exposed as syscalls — userspace threads. When a second flow enters prepare_fds() while ctx.nfds is already 1, the write lands one element past the array; by struct layout it overlaps the adjacent ctx.sock/ctx.nfds members. More broadly, the unsynchronized sharing lets two flows interleave connection setup and teardown, double-closing a socket descriptor or scribbling the shared buffers. The result is corruption of the update subsystem's internal state and denial of service of the firmware-update path; the out-of-bounds write is contained within the ctx structure and there is no demonstrated path to memory outside it or to code execution. Triggering requires a local actor able to invoke update operations (or, with CONFIG_USERSPACE, an unprivileged userspace thread) and to win a timing race against the background handler; remote peers cannot control the race timing. The fix serializes the entry points with a mutex and adds a bounds check to prepare_fds().

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "2.5",
  "pubDate": "2026-08-10T23:16:51.020Z",
  "pubdate": "2026-08-10T23:16:51.020Z",
  "executiveSummary": "An unmitigated concurrency vulnerability exists within the UpdateHub management subsystem, specifically located in subsys/mgmt/updatehub/updatehub.c. The vulnerability arises due to a lack of serialization when accessing a shared file-scope context structure (ctx) alongside a missing bounds check in the prepare_fds() function. This flaw allows two independent execution flows—specifically the background autohandler running on the system workqueue and user-triggered operations via the updatehub run shell command, direct API calls, or userspace threads—to mutate the shared ctx concurrently.\nWhen a race condition is successfully triggered, it results in an out-of-bounds write via ctx.fds[ctx.nfds], leading to memory corruption contained within the adjacent members of the ctx structure, such as ctx.sock and ctx.nfds. Furthermore, unsynchronized sharing leads to race conditions during connection setup and teardown, causing potential double-closing of socket descriptors and buffer scribbling.\nThe primary impact of this vulnerability is a denial of service (DoS) affecting the firmware-update path and corruption of the subsystem's internal state. Successful exploitation requires a local actor capable of invoking update operations—or an unprivileged userspace thread when CONFIG_USERSPACE is enabled—who can successfully win a timing race against the background handler. Remote threat actors cannot control the race timing.\nRisk implications include operational disruption of firmware updates on affected devices. Remediation requires implementing proper synchronization using a mutex to serialize entry points and enforcing strict bounds checking within prepare_fds().",
  "technicalDetails": "The vulnerability resides in the UpdateHub management subsystem implementation within the subsys/mgmt/updatehub/updatehub.c file. The core architectural flaw is the reliance on a single file-scope ctx structure that maintains the state for update operations, including the CoAP block context, payload buffer, status code, socket, and a one-element poll-fd array designated as fds[1].\nTwo distinct and independent execution paths mutate the shared ctx structure concurrently without any synchronization primitives: the background autohandler executing on the system workqueue, and user-initiated operations accessed through the updatehub run shell command, direct API calls, or unprivileged userspace threads (when CONFIG_USERSPACE is active).\nThe exploitation mechanism centers around a race condition combined with an out-of-bounds array write. Specifically, when a second execution flow enters the prepare_fds() function while ctx.nfds is already populated with a value of 1, the function performs an unchecked write to ctx.fds[ctx.nfds] and increments ctx.nfds without verifying array boundaries. Because of the static layout of the struct, this out-of-bounds write lands directly on adjacent members, specifically overlapping ctx.sock and ctx.nfds.\nIn addition to the out-of-bounds memory corruption within the structure, the lack of synchronization enables race conditions during network connection setup and teardown phases. This interleaving can cause the subsystem to double-close socket descriptors or overwrite shared payload buffers.\nThe step-by-step attack flow proceeds as follows: First, a local actor or userspace thread initiates an update operation while the background autohandler is actively processing or about to process an update task. Second, the concurrent execution flows both attempt to modify or interact with the shared ctx structure. Third, the second thread invokes prepare_fds() while ctx.nfds equals 1, triggering the unchecked write past the boundaries of the fds array. Fourth, the adjacent structure members (ctx.sock and ctx.nfds) are corrupted, or a double-close/buffer scribble occurs due to interleaved socket operations.\nPost-exploitation impact is strictly constrained to internal state corruption of the update subsystem and denial of service of the firmware-update mechanism. There is no demonstrated path from this vulnerability to arbitrary memory reads or writes outside the ctx structure, nor is there a path to arbitrary code execution. Exploitation is limited to local actors who can interact with the update subsystem and achieve precise timing against the background handler, as remote threat actors lack the ability to control the race timing."
}