CVE-2026-68453: 
Linux Kernel vulnerability analysis and mitigation

CVE-2026-68453 is a buffer over-read vulnerability in the Linux kernel's s390/zcrypt module, specifically in the cca_cipher2protkey function. The flaw arises from insufficient validation of user-controlled length fields in CCA token structures, allowing an attacker to read beyond buffer boundaries or trigger buffer under-runs. Affected kernel versions begin at commit 4bc123b18ce6ae6c42c69d0456b5acbd2f7bc8bd (from Linux 5.4 onward) and are fixed in Linux 6.18.44, 7.1.8, and 7.2-rc6. It carries a CVSS v3.1 base score of 7.1 (High) (GitHub Advisory, Red Hat Bugzilla).

The root cause is an out-of-bounds read (CWE-125) in the cca_check_sec*token() functions within the s390/zcrypt subsystem. CCA token structures passed by users contain len fields that were used in memory operations without being validated against the actual buffer size or the minimum token structure size. An attacker can craft a token with an oversized len field to read kernel memory beyond the buffer boundary, or supply an undersized len to cause a buffer under-run with similar effects. Additionally, cca_gencipherkey() lacked a check for possible integer underflow with the returned key size. The fix enforces that the key buffer length is at least sizeof the token struct, and that the internal len field falls within the range [sizeof(token struct), key buf length] (GitHub Advisory, Red Hat Bugzilla).

Successful exploitation can result in disclosure of sensitive kernel memory contents or a kernel crash (denial of service). An attacker with local access and the ability to interact with the s390/zcrypt crypto card interface can read arbitrary kernel memory regions, potentially exposing cryptographic key material or other sensitive data processed by the crypto subsystem. The integrity impact is rated None, but the combination of high confidentiality and high availability impact makes this a significant risk on IBM Z (s390x) systems running affected kernel versions (GitHub Advisory).

Exploitation requires local access with low privileges (PR:L) and no user interaction, making it accessible to any unprivileged local user with access to the s390/zcrypt interface. As of the time of disclosure, there is no public proof-of-concept exploit and no evidence of in-the-wild exploitation (GitHub Advisory). The EPSS score is reported as 0.0, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog. Nessus plugin 335232 has been released to detect affected systems (Tenable).

1. Reconnaissance: Identify a target IBM Z (s390x) system running a Linux kernel version from 5.4 up to (but not including) the patched versions (6.18.44, 7.1.8, or 7.2-rc6) with the zcrypt module loaded and accessible.
2. Gain local access: Obtain a low-privileged local account on the target system with access to the /dev/zcrypt or related crypto device interface.
3. Craft malicious CCA token: Construct a CCA token structure with a manipulated len field — either set larger than the actual buffer size (to trigger over-read) or set smaller than sizeof the token struct (to trigger under-run).
4. Submit token via zcrypt interface: Issue an ioctl or equivalent system call to the zcrypt subsystem (e.g., targeting cca_cipher2protkey or related functions) passing the crafted token as input.
5. Trigger memory disclosure or crash: The kernel processes the token without proper bounds checking, reading beyond the buffer boundary and potentially returning sensitive kernel memory contents, or crashing the kernel if an invalid memory region is accessed (GitHub Advisory, Red Hat Bugzilla).

• Logs: Unexpected kernel oops or panic messages referencing cca_cipher2protkey, cca_check_sec*token, or cca_gencipherkey in /var/log/kern.log or dmesg output.
• Process: Unusual processes or scripts running as low-privileged users making repeated ioctl calls to /dev/zcrypt or /dev/z90crypt.
• File System: Unexpected user-space programs or scripts in temporary directories that interact with the zcrypt device interface.
• Network: On systems where crypto card output is forwarded, anomalous data patterns in crypto card request/response logs that may indicate memory content leakage.

Update the Linux kernel to a patched version: 6.18.44, 7.1.8, or 7.2-rc6 (or later), which include fixes at commits a57fd7fcdb63e2d5ceac78bbe825ec986062a9da, 3b2abee2a678607ae27975bc6833785c2002df43, and 36b230835b8a008266aad22168ca52afacc8a58d respectively (GitHub Advisory). As a workaround where patching is not immediately possible, restrict access to the s390/zcrypt interface (/dev/zcrypt, /dev/z90crypt) to only trusted users and processes using appropriate file permissions or Linux access controls (e.g., udev rules, SELinux/AppArmor policies). Red Hat has tracked this issue and users of RHEL on IBM Z should monitor for updated kernel packages (Red Hat Bugzilla).