Executive Summary

CVE-2026-28529 is a use-after-free (UAF) vulnerability in the cryptodev-linux kernel module, specifically in the get_userbuf function of the /dev/crypto device driver. This flaw occurs due to improper handling of page references when managing userland memory pages for cryptographic operations.

The vulnerability arises when the function incorrectly decrements the reference counts of user pages multiple times, leading to premature freeing of pages that are still mapped in the process's page tables. This creates a powerful use-after-free primitive that attackers can exploit to corrupt kernel memory.

Attackers with local access to /dev/crypto can trigger this condition by crafting IOCTL calls that cause the kernel to release user pages prematurely. Exploitation involves manipulating kernel memory allocation behavior and spraying kernel objects to escalate privileges.

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Impact Analysis

This vulnerability allows a local attacker with access to the /dev/crypto interface to escalate their privileges on the affected system.

By exploiting the use-after-free bug, an attacker can gain arbitrary kernel memory corruption capabilities, enabling them to modify critical kernel objects.

Specifically, the exploit can modify file mode flags on kernel file objects to gain write permissions on sensitive files like /etc/passwd, allowing the attacker to add a new root user and obtain full root access.

This results in a local privilege escalation (LPE), compromising the confidentiality, integrity, and availability of the system.

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Detection Guidance

Detection of CVE-2026-28529 involves monitoring for suspicious activity related to the /dev/crypto device and anomalous memory or file operations indicative of use-after-free exploitation attempts.

Specifically, detection can focus on the following:

• Monitoring IOCTL calls to /dev/crypto, especially repeated or malformed CIOCGSESSION and CIOCCRYPT calls that could trigger the vulnerability.
• Checking for abnormal memory allocation and deallocation patterns, such as large numbers of mmap and munmap calls (e.g., allocating and freeing hundreds of thousands of pages).
• Observing a high number of file descriptors opened to sensitive files like /etc/passwd, which may indicate struct file spraying attempts.

Suggested commands for detection include:

• Use `lsof | grep /etc/passwd` to detect an unusually large number of open file descriptors to /etc/passwd.
• Use `strace` on processes interacting with /dev/crypto to monitor IOCTL calls, for example: `strace -e trace=ioctl -p <pid>`.
• Monitor kernel logs for KASAN (Kernel Address Sanitizer) reports or slab-use-after-free errors related to cryptodev-linux functions such as `__get_userbuf`.
• Use `dmesg | grep -i cryptodev` or `journalctl -k | grep -i cryptodev` to check for kernel warnings or errors.

Note that detection requires kernel-level monitoring and may involve custom scripts to identify the specific patterns of exploitation described.

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Mitigation Strategies

Immediate mitigation steps for CVE-2026-28529 focus on preventing exploitation of the use-after-free vulnerability in cryptodev-linux's /dev/crypto device driver.

• Restrict access to /dev/crypto to trusted users only, minimizing the risk of local attackers triggering the vulnerability.
• Apply any available patches or updates to cryptodev-linux that address the vulnerability, including fixes for reference count handling and asynchronous task synchronization.
• If patches are not immediately available, consider disabling or unloading the cryptodev-linux kernel module to prevent use of /dev/crypto.
• Monitor system logs for suspicious activity related to /dev/crypto and unusual file descriptor usage patterns.
• Limit the number of open file descriptors and memory allocations per user to reduce the feasibility of spraying attacks.

Long-term mitigation involves updating the kernel and cryptodev-linux module to versions that include the fixes for this vulnerability, which address the root causes such as improper page reference handling and asynchronous work synchronization.

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Compliance Impact

CVE-2026-28529 is a local privilege escalation vulnerability in the cryptodev-linux kernel module that allows an attacker with local access to gain root privileges by exploiting a use-after-free bug. This can lead to unauthorized modification of critical system files such as /etc/passwd, enabling creation of new root users and full system compromise.

Such a vulnerability poses significant risks to compliance with common standards and regulations like GDPR and HIPAA, which mandate strict controls on access to sensitive data and system integrity. Successful exploitation could lead to unauthorized access, data breaches, and tampering with system audit logs or security controls, thereby violating confidentiality, integrity, and availability requirements.

Organizations using affected versions of cryptodev-linux must consider this vulnerability a critical security risk that could undermine compliance efforts, necessitating prompt patching and mitigation to maintain regulatory adherence.

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