Description

In the Linux kernel, the following vulnerability has been resolved: s390/zcrypt: Validate length for CCA AES cipher key requests cca_cipher2protkey() derives the copy length for the CPRB parameter block directly from the length field in the key token. Reject the request early if the token length exceeds the available space in the parameter block.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.8",
  "pubDate": "2026-08-13T15:19:57.970Z",
  "pubdate": "2026-08-13T15:19:57.970Z",
  "executiveSummary": "A vulnerability exists in the Linux kernel s390 zcrypt subsystem concerning the handling of CCA AES cipher key requests. Specifically, the function cca_cipher2protkey() derives the copy length for the CPRB parameter block directly from the length field embedded within the key token without performing adequate validation against the bounds of the available buffer space in the parameter block.\nThis vulnerability constitutes an insufficient input validation issue that can lead to out-of-bounds memory copy operations, potentially resulting in kernel memory corruption, system crashes, or denial of service conditions. The affected systems are Linux kernel deployments utilizing the s390 architecture with zcrypt hardware acceleration and cryptographic coprocessor support.\nExploitation of this vulnerability requires an attacker to possess the capability to submit malformed or maliciously crafted CCA AES cipher key tokens to the zcrypt subsystem, typically requiring local access or interaction with cryptographic device interfaces exposed to user space applications.",
  "technicalDetails": "The root cause of the vulnerability resides in the cca_cipher2protkey() function within the s390 zcrypt subsystem of the Linux kernel. When processing CCA AES cipher key requests, the function extracts the copy length parameter for the Cryptographic Parameter Request Block (CPRB) directly from a length field supplied inside the key token data structure.\nDue to the absence of boundary checks verifying whether the extracted token length exceeds the actual allocated space within the parameter block, a crafted request containing an excessively large length value causes the kernel to attempt copying more data than the destination buffer can accommodate.\nThe attack flow proceeds as follows: First, an attacker constructs a malicious CCA AES cipher key token where the internal length field is manipulated to specify a size greater than the maximum bounds of the CPRB parameter block. Second, the attacker submits this crafted key token via the zcrypt device driver interface to the kernel. Third, the vulnerable cca_cipher2protkey() function reads the oversized length field without validation. Fourth, the subsequent memory operation copies data beyond the allocated bounds of the parameter block, triggering memory corruption within kernel space.\nThe vulnerable component is the s390 zcrypt subsystem, specifically the cca_cipher2protkey() routine responsible for translating CCA cipher keys into protected keys. The vulnerability affects Linux kernel implementations running on IBM s390 architectures that utilize cryptographic coprocessors. Exploitation may lead to kernel panics, system instability, or potential denial of service affecting the cryptographic infrastructure of the host operating system."
}