CVE-2026-28529: cryptodev-linux Privilege Escalation Flaw

CVE-2026-28529 Overview

CVE-2026-28529 is a use-after-free vulnerability in the cryptodev-linux kernel module that allows local privilege escalation. The flaw exists in the get_userbuf function within the /dev/crypto device driver, where improper page reference handling enables attackers to trigger dangerous memory conditions. Local users with access to the /dev/crypto interface can exploit this vulnerability by repeatedly decrementing reference counts of controlled pages, ultimately achieving elevated privileges on the system.

Critical Impact

Local attackers with access to the /dev/crypto interface can exploit this use-after-free condition to escalate privileges and gain root access on affected Linux systems running cryptodev-linux version 1.14 or earlier.

Affected Products

• cryptodev-linux version 1.14
• cryptodev-linux versions prior to 1.14
• Linux systems with the /dev/crypto device driver enabled

Discovery Timeline

• 2026-03-25 - CVE-2026-28529 published to NVD
• 2026-03-25 - Last updated in NVD database

Technical Details for CVE-2026-28529

Vulnerability Analysis

This use-after-free vulnerability (CWE-416) exists in the cryptodev-linux kernel module's get_userbuf function. The core issue involves improper management of page reference counts when handling user-supplied buffers through the /dev/crypto interface. When the driver processes cryptographic operations, it pins user memory pages and manages their reference counts. However, a flaw in this logic allows attackers to manipulate the reference counting mechanism.

The vulnerability enables local attackers to repeatedly decrement page reference counts for memory regions they control. By carefully crafting sequences of operations against the /dev/crypto device, an attacker can force the reference count to reach zero prematurely, causing the kernel to free the page while it's still in use. Subsequent access to this freed memory creates a classic use-after-free condition.

This memory corruption primitive can be leveraged to achieve arbitrary kernel memory read/write capabilities, ultimately leading to complete system compromise through local privilege escalation to root.

Root Cause

The root cause lies in the get_userbuf function's failure to properly track and synchronize page reference counts during cryptographic operations. When user buffers are pinned for kernel access, the reference counting logic does not adequately prevent underflow conditions. This allows an attacker to craft specific sequences of cryptographic requests that cause reference counts to be decremented more times than they were incremented, resulting in premature page deallocation.

Attack Vector

This is a local attack vector requiring the attacker to have user-level access to the system and the ability to interact with the /dev/crypto device interface. The attack follows this general pattern:

1. Initial Access: Attacker gains local user access to a system with cryptodev-linux loaded
2. Device Interaction: Attacker opens the /dev/crypto device and initiates cryptographic operations with carefully crafted user buffers
3. Reference Count Manipulation: Through repeated operations, the attacker causes page reference counts to decrement below their expected values
4. Use-After-Free Trigger: When reference counts reach zero, the kernel frees pages that are still mapped in the attacker's address space
5. Memory Corruption: The attacker can now manipulate the contents of freed pages to achieve arbitrary kernel memory access
6. Privilege Escalation: The attacker modifies kernel structures to elevate privileges to root

Technical details and proof-of-concept information can be found in the security researcher's post and the associated GitHub Gist.

Detection Methods for CVE-2026-28529

Indicators of Compromise

• Unusual activity involving the /dev/crypto device, particularly rapid or repeated cryptographic operations from non-standard processes
• Kernel log entries indicating memory corruption, double-free conditions, or page reference count anomalies
• Unexpected privilege escalation events where user processes gain root access
• Processes accessing /dev/crypto that don't typically perform cryptographic operations

Detection Strategies

• Monitor system calls to the /dev/crypto device interface using kernel auditing (auditd) or eBPF-based monitoring
• Implement anomaly detection for processes accessing hardware cryptographic interfaces without legitimate business needs
• Deploy kernel integrity monitoring to detect unauthorized modifications to privilege-related structures
• Use SentinelOne's behavioral AI engine to identify suspicious privilege escalation patterns following cryptographic device access

Monitoring Recommendations

• Enable kernel audit logging for all /dev/crypto device access with rules targeting open, ioctl, and mmap syscalls
• Implement real-time alerting for any privilege escalation events on systems where cryptodev-linux is deployed
• Monitor for kernel oops or panic events that may indicate failed exploitation attempts
• Review process lineage for any root-level processes that originated from user sessions interacting with /dev/crypto

How to Mitigate CVE-2026-28529

Immediate Actions Required

• Review the fix implemented in the official pull request and apply the patch to affected systems
• Restrict access to the /dev/crypto device by modifying device permissions or using device control policies
• Consider temporarily unloading the cryptodev-linux module (rmmod cryptodev) on systems where it's not actively required
• Audit systems to identify which services and applications depend on /dev/crypto functionality

Patch Information

A fix for this vulnerability has been developed and is available through the cryptodev-linux GitHub repository pull request #104. Organizations running affected versions should review this patch and apply it to their kernel module builds. For systems using distribution-provided packages, monitor your distribution's security advisories for updated cryptodev-linux packages.

Additional technical analysis is available from the VulnCheck advisory.

Workarounds

• Remove or restrict access to /dev/crypto by changing device permissions: chmod 600 /dev/crypto and ensuring only root can access it
• Blacklist the cryptodev module to prevent automatic loading by adding blacklist cryptodev to /etc/modprobe.d/blacklist.conf
• Implement SELinux or AppArmor policies to restrict which processes can interact with the /dev/crypto device
• Use container isolation to limit exposure of the cryptographic device to only trusted workloads that require it

# Restrict /dev/crypto access to root only
chmod 600 /dev/crypto
chown root:root /dev/crypto

# Prevent automatic module loading (add to /etc/modprobe.d/blacklist-cryptodev.conf)
echo "blacklist cryptodev" >> /etc/modprobe.d/blacklist-cryptodev.conf

# Unload the module if not needed
rmmod cryptodev