Description

Use-After-Free vulnerability in a zircon kernel pager proxy (Fuchsia), which could lead to a Privilege Escalation from Userspace to Kernel (AP)

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "8.8",
  "pubDate": "2026-08-24T17:17:21.303Z",
  "pubdate": "2026-08-24T17:17:21.303Z",
  "executiveSummary": "A Use-After-Free (UAF) vulnerability exists within the zircon kernel pager proxy in the Fuchsia operating system. This memory corruption flaw allows a malicious actor operating from userspace to achieve Privilege Escalation up to the kernel execution context (Application Processor).\nThe vulnerability impacts the core zircon kernel architecture, specifically within pager proxy operations where improper object lifecycle management or reference counting occurs. If successfully exploited, an attacker with local userspace access can manipulate dangling memory pointers to corrupt kernel heap structures, execute arbitrary code with kernel privileges, and completely compromise the integrity and confidentiality of the affected Fuchsia system.\nExploitation requires initial local execution access within the userspace environment of the Fuchsia operating system, meaning remote attackers cannot directly exploit this flaw without a prior execution vector. The risk implications are severe due to the potential for full system compromise, breaking the isolation boundary between userspace processes and the zircon kernel.",
  "technicalDetails": "The vulnerability resides in the zircon kernel pager proxy mechanism within the Fuchsia operating system, stemming from improper lifecycle management of kernel objects associated with memory paging operations. Specifically, a Use-After-Free condition occurs when a pager proxy object or its underlying state is deallocated while references to it remain active within kernel data structures.\nThe root cause is a failure in the reference counting or synchronization logic governing the pager proxy interface. When a userspace process interacts with the zircon kernel pager proxy, specific syscalls initiate paging requests and manage memory backing. Due to the flaw, a race condition or improper cleanup sequence allows the kernel to release the memory backing the pager proxy object while pointers to this structure persist in internal kernel lists or context blocks.\nAttack flow begins with an attacker executing a crafted binary or leveraging an existing userspace primitive to interact with the vulnerable zircon kernel pager proxy subsystem. The attacker triggers the creation and subsequent destruction of specific pager proxy mappings in a manner that induces the kernel to retain a dangling pointer to the freed object structure.\nFollowing the deallocation, the attacker performs heap feng-shui or heap grooming from userspace by allocating new kernel objects of a similar size to reclaim the memory region previously occupied by the pager proxy structure. When the kernel subsequently attempts to access the dangling pointer—expecting a valid pager proxy object—it instead reads or writes to the attacker-controlled memory now occupying that slot.\nThis type confusion and arbitrary read/write capability over kernel memory structures enables the attacker to overwrite function pointers, credentials, or critical kernel control data. By carefully crafting the replacement payload in the heap, the attacker hijacks the kernel execution flow, leading to arbitrary code execution with kernel-level privileges (AP).\nAuthentication and privilege requirements for this attack are minimal regarding the kernel interface itself, as standard userspace processes can typically interact with zircon kernel syscalls, though specific capability tokens may be required depending on the sandbox configuration. The vulnerability has no network exposure as it is strictly local to the zircon kernel interface."
}