CVE-2026-58088 in FreeBSD
Summary
by MITRE • 08/19/2026
The ELF core dump code counted the number of dumpable VM map entries, allocated a buffer for the corresponding program headers, then iterated over the map a second time to populate them. A process sharing the address space via rfork(2) can mutate the map between the two passes, causing the second pass to write program headers past the end of the buffer.
An unprivileged local user sharing an address space with a process that dumps core can trigger an out-of-bounds write on the kernel heap, potentially leading to privilege escalation.
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Analysis
by VulDB Data Team • 08/19/2026
The vulnerability described involves a classic race condition within the FreeBSD ELF core dump generation mechanism, specifically affecting processes that share their virtual memory map via rfork(2). The core issue stems from a lack of synchronization between two distinct phases of buffer allocation and population during the creation of a core file. In the first phase, the kernel iterates over the process's VM map entries to count them, subsequently allocating a heap buffer sized exactly for that number of program headers. This approach assumes that the state of the virtual memory map remains static throughout the duration of the dump operation. However, when multiple processes share an address space through rfork(2), they operate on the same underlying data structures without sufficient isolation or locking mechanisms to prevent concurrent modifications during this critical window.
An unprivileged local user can exploit this timing gap by manipulating their shared memory map between the initial counting pass and the subsequent population pass. By adding new mappings or modifying existing ones, the attacker causes the actual number of VM entries at the time of writing to exceed the count obtained earlier. Consequently, when the kernel attempts to populate the pre-allocated buffer with program headers for all current entries, it writes past the end of the allocated heap memory. This results in a heap-based out-of-bounds write, allowing the attacker to overwrite adjacent kernel data structures or metadata stored on the kernel heap.
The operational impact of this vulnerability is severe, as it provides a pathway for privilege escalation from an unprivileged user context to root-level access within the operating system. By carefully crafting the memory layout and controlling what data is written beyond the buffer boundary, an attacker can potentially corrupt critical kernel structures such as function pointers or object headers. This corruption can be leveraged to execute arbitrary code with kernel privileges, effectively compromising the integrity of the entire system. The vulnerability highlights a fundamental flaw in assuming atomicity for complex multi-step operations involving shared mutable state without proper synchronization primitives like read-write locks or copy-on-write semantics during snapshotting processes.
From a classification perspective, this issue aligns with CWE-362, which describes concurrent execution using shared resources with improper synchronization. The specific mechanism of exploiting a race condition to achieve an out-of-bounds write also relates closely to CWE-415, double free or use-after-free in some contexts, though here it is strictly a buffer overflow due to stale state assumptions. In terms of the MITRE ATT&CK framework, this vulnerability facilitates lateral movement and privilege escalation techniques, specifically falling under Tactic TA0004 (Privilege Escalation) and Technique T1068 (Exploitation for Privilege Escalation). The attack vector is local, requiring physical or shell access to the target system, which classifies it as a Local Attack Vector in terms of exploitability.
Mitigation strategies must focus on ensuring that the virtual memory map remains consistent during the core dump generation process. This can be achieved by implementing proper locking mechanisms around the VM map iteration and buffer allocation phases. Specifically, using read-write locks or snapshotting techniques to capture a stable view of the address space before counting entries would prevent mutations from affecting the allocated buffer size. Additionally, adding bounds checking in the second pass to ensure that no more headers are written than were originally allocated can serve as a defensive coding practice to prevent heap corruption even if synchronization fails. System administrators should apply vendor-provided patches immediately upon availability and restrict core dump generation permissions where possible to limit exposure until the underlying code is corrected.