CVE-2026-31912 in libpcap
Summary
by MITRE • 09/05/2026
libpcap BPF interpreter detects neither reaching the end of the filter program buffer due to lack of a return instruction nor executing a jump instruction with an offset that translates to a pointer outside of the buffer. In particular uncommon use cases a crafted filter program can cause the interpreter to try reading the OS process memory in the 32GiB around the buffer on 64-bit architectures and in the entire address space on 32-bit architectures.
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Analysis
by VulDB Data Team • 09/05/2026
The libpcap library, which serves as the foundational packet capture interface for numerous network monitoring tools including Wireshark, tcpdump, and various intrusion detection systems, contains a critical vulnerability within its Berkeley Packet Filter (BPF) interpreter logic. This flaw stems from an insufficient validation mechanism when processing compiled BPF filter programs. Specifically, the interpreter fails to detect two distinct boundary violations: it does not verify whether execution has reached the end of the allocated buffer due to a missing return instruction, and it fails to validate that jump instructions with offsets do not point outside the bounds of the program memory. This lack of rigorous range checking allows crafted or malformed filter programs to bypass standard safety checks embedded within the virtual machine implementation.
The technical nature of this vulnerability involves an out-of-bounds read condition triggered by improper pointer arithmetic during instruction execution. When a BPF jump instruction specifies an offset that, when added to the current program counter, results in an address outside the allocated buffer region, the interpreter does not halt or raise an error. Instead, it proceeds to fetch and execute instructions from memory locations adjacent to or far beyond the intended buffer space. On 64-bit architectures, this allows access to a contiguous range of approximately thirty-two gigabytes surrounding the filter program buffer. In contrast, on 32-bit systems where address spaces are more constrained but still vulnerable due to the lack of bounds checking, the interpreter may attempt to read from anywhere within the entire process memory space. This behavior effectively transforms a simple packet filtering mechanism into an arbitrary memory read primitive.
The operational impact of this vulnerability is severe, primarily because it enables information disclosure and potentially remote code execution depending on the context in which libpcap operates. By reading unintended memory regions, an attacker can extract sensitive data such as cryptographic keys, session tokens, or other confidential process information residing near the buffer location. Furthermore, if the application utilizing libpcap allows user-supplied filter programs to be loaded dynamically from untrusted sources, this flaw could facilitate more complex exploitation chains. The ability to read arbitrary memory increases the attack surface significantly, allowing attackers to gather intelligence about the running environment or potentially leak data that should remain isolated within the process boundaries. This is particularly dangerous in network monitoring appliances and security sensors where large volumes of packet capture buffers are allocated dynamically during runtime.
This vulnerability aligns with CWE-125, which describes Out-of-bounds Read vulnerabilities, as it involves accessing memory locations beyond the intended buffer limits without proper validation. Additionally, from a tactical perspective related to the MITRE ATT&CK framework, this flaw facilitates Data Staged and Collection activities by allowing unauthorized access to process memory contents. It also relates to CWE-20 Improper Input Validation, as the core failure lies in the inability of the BPF interpreter to correctly validate the structural integrity and logical boundaries of the input filter program before execution. The lack of a return instruction check further exacerbates this issue by allowing control flow to escape the designated code segment entirely.
Mitigation strategies must focus on both immediate patching and long-term architectural improvements. Organizations relying on libpcap should immediately update to versions that include patches addressing these boundary checks in the BPF interpreter logic. Developers integrating libpcap into their applications must ensure they are using updated library versions across all deployment environments, including embedded devices and server infrastructure. For those unable to patch immediately, implementing strict input validation for any user-supplied BPF filter programs is critical; this includes verifying that filters do not contain jump instructions with excessive offsets or missing termination sequences before passing them to the pcap_compile function. Additionally, deploying network segmentation and monitoring solutions can help detect anomalous memory access patterns or unusual packet capture activities that might indicate exploitation attempts against vulnerable systems.