ARM Mali GPU Kernel Driver Use-After-Free Vulnerability (CVE-2021-29256) Analysis and Mitigation Guide
Executive & SecOps Summary
SECOPS ASSESSMENTARM Mali GPU kernel driver Bifrost (r16p0 through r29p0), Valhall (r19p0 through r29p0), and Midgard (r28p0 through r30p0)
An unprivileged local attacker can exploit a Use-After-Free (UAF) condition to access freed memory, leading to sensitive information disclosure or root privilege escalation
Apply the official security patches from chipset vendors and OEMs, upgrading the Mali GPU kernel driver to version r30p0 or higher
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
According to the ARM security advisory, the driver must be updated to version r30p0 or higher. Integrate the updated Mali GPU driver source into your kernel build environment.
# Clone the updated Mali GPU kernel driver source (r30p0)
git clone https://github.com/ARM-software/mali-ddk-kernel-driver.git -b r30p0
# Replace the legacy driver source in your kernel tree and rebuild
make ARCH=arm64 defconfig
make ARCH=arm64 -j$(nproc)2. Temporary Workaround & Hardening Configuration
If immediate patching is not feasible, restrict access to the GPU device node to minimize the attack surface.
# Restrict permissions on the Mali GPU device node to root only
chmod 600 /dev/mali0
# Example: Tighten SELinux policies to deny untrusted apps access to the GPU device
# (Modify the appropriate .te policy file in your Android build)
# deny untrusted_app gpu_device:chr_file rw_file_perms;3. Log Audit & IoC Verification Commands
Verify the currently loaded Mali GPU driver version and inspect system logs for potential exploitation attempts or driver crashes.
# Check the active Mali GPU driver version
cat /sys/module/mali/version
cat /sys/module/mali_kbase/version
# Search system logs for Mali-related errors or Use-After-Free indicators
dmesg | grep -Ei 'mali|uaf|use-after-free|page fault'Block Kernel Privilege Escalation & Ransomware Payloads Before You Can Reboot
Protect unpatched Windows, Linux, and macOS workloads against in-memory exploitation and lateral movement with autonomous EDR.
Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2021-29256) is a Use-After-Free (UAF) flaw within the ARM Mali GPU kernel driver. The root cause lies in the driver's memory management and mapping routines, where references to allocated memory blocks are not properly invalidated after being freed. This allows an unprivileged local user to interact with the dangling pointers and access the freed memory space.
2. Exploitation Mechanics & Attack Scenario
An attacker begins by gaining local, unprivileged execution access on the target device (e.g., via a malicious application or local shell). By invoking specific system calls targeting the Mali GPU driver interface (such as /dev/mali0), the attacker triggers the allocation and subsequent deallocation of memory objects. By exploiting the UAF condition, the attacker can manipulate the contents of the freed memory block, overwrite kernel structures, and escalate privileges to root.
3. Infrastructure & Business Impact
As this vulnerability is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, it represents a highly critical threat with confirmed active exploitation in the wild. Since ARM Mali GPUs are widely integrated into Android smartphones, smart TVs, and IoT devices, unpatched endpoints pose a severe risk of full device compromise, potentially serving as an entry point for lateral movement within corporate networks.
Official Vendor Advisories & References
. The Arm Mali GPU kernel driver allows an unprivileged user to achieve access to freed memory, leading to information disclosure or root privilege escalation. This affects Bifrost r16p0 through r29p0 before r30p0, Valhall r19p0 through r29p0 before r30p0, and Midgard r28p0 through r30p0.
Frequently Asked SecOps Questions (CVE-2021-29256)
FAQQ1. How critical is CVE-2021-29256 and is it actively exploited in the wild?
CVE-2021-29256 is rated CVSS 8.8 (HIGH) with a 30-day EPSS exploitation probability of 3.0%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2021-29256?
Primary impacted vendors include arm across mali gpu kernel driver. Scope summary: ARM Mali GPU Kernel Driver: - Bifrost: r16p0 through r29p0 (before r30p0) - Valhall: r19p0 through r29p0 (before r30p0) - Midgard: r28p0 through r30p0
Q3. What temporary mitigations or workarounds exist for CVE-2021-29256 before patching?
[Mitigation] Apply the official security patches from chipset vendors and OEMs, upgrading the Mali GPU kernel driver to version r30p0 or higher Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
Generate an Internal Engineering Notice or CISO Report for CVE-2021-29256
Instantly format this advisory into an executive CISO summary or engineering patch ticket.
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