CVE-2026-68451 in Linux
Summary
by MITRE • 08/13/2026
In the Linux kernel, the following vulnerability has been resolved:
s390/zcrypt: Validate length for CCA ECC private key requests
cca_ecc2protkey() 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.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 08/26/2026
The vulnerability identified in the Linux kernel s390/zcrypt subsystem represents a critical buffer overflow condition that could be exploited to compromise system integrity. This issue specifically affects the cryptographic operations performed on IBM System/390 mainframe systems where the zcrypt driver handles cryptographic acceleration for CCA (Cryptographic Coprocessor Algorithm) elliptic curve cryptography operations. The flaw resides in how the cca_ecc2protkey() function processes private key requests, where it directly uses the length field from a key token to determine the copy length for the CPRB (Crypto Parameter Request Block) parameter structure without proper validation against available buffer space.
The technical implementation of this vulnerability stems from inadequate input validation within the cryptographic subsystem. When processing elliptic curve private key requests, the function extracts the length information directly from the key token header and uses it as a direct copy size parameter for the CPRB block. This approach creates a potential for arbitrary code execution or system crash when an attacker provides a malformed key token with an oversized length field that exceeds the physical boundaries of the parameter block structure. The vulnerability manifests as a classic buffer overflow condition where the system attempts to copy more data than the allocated buffer can accommodate, potentially overwriting adjacent memory regions and corrupting kernel data structures.
The operational impact of this vulnerability extends beyond simple denial of service scenarios to encompass potential privilege escalation and system compromise within environments utilizing IBM mainframe systems with Linux kernel cryptographic acceleration. Attackers could exploit this weakness to execute malicious code in kernel space, potentially gaining administrative privileges or causing persistent system instability that would require complete system reboot for recovery. The attack vector requires access to the cryptographic subsystem and knowledge of the specific CCA ECC private key token format, making it somewhat specialized but still viable in targeted attacks against mainframe environments where such cryptographic operations are actively utilized.
Security mitigations for this vulnerability involve implementing early validation checks within the cca_ecc2protkey() function to verify that the key token length does not exceed the maximum allowable size for the CPRB parameter block before any copying operations occur. The fix requires adding bounds checking logic that compares the length field from the token against the actual buffer capacity and returns an error code when validation fails. This approach aligns with common security practices outlined in the CWE (Common Weakness Enumeration) catalog under weakness category 129 which addresses insufficient input validation, and also follows ATT&CK framework techniques for privilege escalation through kernel exploits. The solution demonstrates proper defensive programming principles by implementing input sanitization before data processing operations, preventing the overflow condition from occurring at its source rather than attempting to recover from it after the fact. Organizations should prioritize applying this patch across all mainframe systems utilizing zcrypt acceleration to prevent exploitation of this vulnerability that could lead to unauthorized system access and data compromise in high-value enterprise environments.