CVE-2022-49873 in Linux
Summary
by MITRE • 05/01/2025
In the Linux kernel, the following vulnerability has been resolved:
bpf: Fix wrong reg type conversion in release_reference()
Some helper functions will allocate memory. To avoid memory leaks, the verifier requires the eBPF program to release these memories by calling the corresponding helper functions.
When a resource is released, all pointer registers corresponding to the resource should be invalidated. The verifier use release_references() to do this job, by apply __mark_reg_unknown() to each relevant register.
It will give these registers the type of SCALAR_VALUE. A register that will contain a pointer value at runtime, but of type SCALAR_VALUE, which may allow the unprivileged user to get a kernel pointer by storing this register into a map.
Using __mark_reg_not_init() while NOT allow_ptr_leaks can mitigate this problem.
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Analysis
by VulDB Data Team • 08/15/2025
The vulnerability identified as CVE-2022-49873 resides within the Linux kernel's eBPF (extended Berkeley Packet Filter) subsystem, specifically in the bpf verifier component responsible for validating eBPF programs before execution. This flaw represents a critical security issue that could potentially allow unprivileged users to extract kernel pointers through improper register type handling during memory release operations. The vulnerability stems from incorrect type conversion in the release_reference() function, which is part of the eBPF verifier's memory management logic. When helper functions allocate memory within eBPF programs, the verifier mandates that these resources be explicitly released using corresponding helper functions to prevent memory leaks. The system employs a mechanism called release_references() to invalidate pointer registers associated with released resources, ensuring that no dangling pointers remain accessible to user-space programs.
The technical flaw manifests when the verifier attempts to invalidate registers containing pointer values by applying __mark_reg_unknown() to convert them to SCALAR_VALUE type. This conversion process creates a dangerous condition where registers that should contain pointer values at runtime are marked as scalar values, effectively allowing unprivileged users to store these registers into eBPF maps. The resulting exposure enables attackers to potentially extract kernel memory addresses, which could be leveraged for privilege escalation or information disclosure attacks. This particular vulnerability is classified as a type confusion issue where the register type system fails to properly enforce the distinction between pointer and scalar value types during memory cleanup operations. The flaw directly relates to CWE-121 and CWE-122 categories, representing buffer overflow conditions and heap-based buffer overflow vulnerabilities respectively, as the improper handling of register types can lead to memory corruption and unauthorized access to kernel space.
The operational impact of this vulnerability extends beyond simple information disclosure, as it creates a potential pathway for privilege escalation attacks within the kernel's eBPF execution environment. An unprivileged user could exploit this flaw by crafting malicious eBPF programs that manipulate register types during memory release operations, ultimately extracting kernel pointers that could be used to bypass kernel security controls. The vulnerability affects systems running Linux kernels with eBPF support, particularly those implementing security policies that rely on eBPF for network filtering, system monitoring, or application security enforcement. Attackers could potentially use the extracted kernel pointers to perform advanced exploitation techniques such as kernel address leaks, which are commonly used in exploitation chains targeting other kernel vulnerabilities. This vulnerability also aligns with ATT&CK technique T1068, which describes the use of privilege escalation through kernel exploits, and T1059, representing the execution of malicious code through legitimate system processes.
The recommended mitigation strategy involves implementing the use of __mark_reg_not_init() function when the NOT allow_ptr_leaks flag is active, which prevents the problematic type conversion that leads to kernel pointer exposure. System administrators should ensure their Linux kernels are updated to versions that include the patched release_references() function, which properly handles register type conversions during memory release operations. Additionally, organizations should consider implementing eBPF program validation policies that restrict the execution of potentially malicious eBPF programs, particularly those that attempt to manipulate register types or perform memory management operations. The fix specifically addresses the verifier's handling of pointer registers during resource cleanup, ensuring that pointer registers maintain their correct type information even when the associated memory has been released. This patch demonstrates the critical importance of proper type system enforcement in kernel security mechanisms, as the incorrect handling of register types can create security boundaries that are easily exploited by unprivileged users. Organizations should also monitor their eBPF program deployment practices to ensure that only trusted and properly validated programs are executed within systems that may be vulnerable to such register type manipulation attacks.