Description

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.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "5.5",
  "pubDate": "2026-09-05T19:16:55.823Z",
  "pubdate": "2026-09-05T19:16:55.823Z",
  "executiveSummary": "The libpcap Berkeley Packet Filter (BPF) interpreter contains a critical vulnerability related to insufficient bounds checking of filter programs. This flaw allows a crafted BPF bytecode program to bypass memory safety constraints, enabling unauthorized out-of-bounds read operations.\nThe vulnerability stems from the interpreter failing to validate two critical conditions: the presence of a mandatory return instruction at the end of the filter program and the range of jump instruction offsets. Because the interpreter does not verify these offsets against the buffer boundaries, it can be forced to resolve addresses pointing outside the designated program memory.\nOn 64-bit architectures, this permits an attacker to read up to 32GiB of process memory surrounding the BPF buffer. On 32-bit architectures, the impact extends to the entire accessible address space of the process. An attacker with the ability to load a crafted packet filter can leverage this vulnerability to perform unauthorized memory reads, potentially leaking sensitive information, cryptographic keys, or process-specific data from the host application. The risk is significant, as it violates the memory isolation guarantees expected of the BPF virtual machine within libpcap.\nExploitation requires the ability to supply a custom BPF filter program to the library, typically seen in applications that process network traffic based on user-provided rules.",
  "technicalDetails": "The root cause of this vulnerability lies in the logic of the BPF bytecode interpreter within libpcap. The interpreter fails to perform two fundamental security checks during the execution cycle: validation of the program termination (guaranteeing a return instruction exists) and validation of jump offsets (ensuring the control flow remains within the allocated instruction buffer).\nIn the BPF virtual machine architecture, the instruction pointer should never increment past the boundary of the loaded filter buffer. However, due to the missing bounds check, a crafted jump instruction can specify an offset that, when added to the current instruction pointer, results in a memory address residing outside the valid heap or stack region where the filter resides. Because the interpreter uses this calculated pointer to fetch the next instruction, it effectively treats external memory as executable bytecode.\nThe attack flow proceeds as follows: First, the attacker supplies a malicious BPF program containing specifically crafted jump instructions. Second, the libpcap interpreter loads this program into memory. Third, the interpreter begins execution. When the malicious jump instruction is encountered, the interpreter calculates the target offset, which points to arbitrary memory space rather than the legitimate buffer. Finally, the interpreter attempts to 'fetch' and execute instructions from this unauthorized address space. As the interpreter processes these memory locations as if they were BPF instructions, it creates a side-channel or a direct read mechanism, allowing an attacker to interpret process memory and extract data contained within the reachable address space.\nOn 64-bit systems, the pointer arithmetic allows the interpreter to access memory within a 32GiB window around the buffer, while 32-bit systems allow full access to the process address space. This bypasses the intended sandbox limitations of the BPF interpreter. The impact is primarily information disclosure; by carefully crafting the 'instructions' read from the process memory, an attacker can coerce the library into performing operations that reveal the contents of the memory being read, such as environment variables, pointers, or stack-resident secrets.\nThis vulnerability is particularly dangerous in high-privilege applications that use libpcap to filter traffic, as the attacker essentially gains an 'oracle' that reads arbitrary memory via the packet filtering mechanism. No authentication or elevated privileges are required beyond the ability to invoke the filter-loading functionality within the target application context."
}