CVE-2026-40257: Trustedfirmware Op-tee Buffer Overflow

CVE-2026-40257 Overview

CVE-2026-40257 is an off-by-one heap overflow in the Open Portable Trusted Execution Environment (OP-TEE). OP-TEE provides a Trusted Execution Environment companion to non-secure Linux kernels on Arm Cortex-A cores using TrustZone. The flaw resides in the ARM Crypto Extensions accelerated SHA-3 implementation. An off-by-one error corrupts TEE kernel memory following the hash state structure. The vulnerability affects OP-TEE versions 3.21.0 through 4.10.x when built with CFG_CRYPTO_WITH_CE82=y. Version 4.11.0 contains the fix.

Critical Impact
A local attacker with low privileges can trigger heap corruption in TEE kernel memory, resulting in high availability impact on the Trusted Execution Environment.

Affected Products

Trusted Firmware OP-TEE versions 3.21.0 through 4.10.x
Platforms built with CFG_CRYPTO_WITH_CE82=y (ARMv8.2+ with SHA-3 Crypto Extensions)
ARM Cortex-A devices using TrustZone with OP-TEE and CE-accelerated SHA-3

Discovery Timeline

2026-07-06 - CVE-2026-40257 published to NVD
2026-07-07 - Last updated in NVD database

Technical Details for CVE-2026-40257

Vulnerability Analysis

The vulnerability is classified as an out-of-bounds write [CWE-787] in the SHA-3 hashing routine accelerated by ARM Crypto Extensions. The implementation contains an off-by-one boundary error that writes past the allocated hash state buffer on the TEE kernel heap. Because SHA-3 processing occurs inside the secure world, corruption propagates through all heap memory following the hash state structure.

The flaw executes locally within the TEE kernel context. Any Trusted Application (TA) or client invoking SHA-3 hashing through the OP-TEE crypto API triggers the faulty accelerated path when CFG_CRYPTO_WITH_CE82=y is enabled at build time. Successful exploitation destabilizes the secure world and can crash TEE services that other applications depend on.

Root Cause

The root cause is an off-by-one indexing error in the CE-accelerated SHA-3 permutation logic. The implementation writes one byte or word beyond the intended boundary of the internal state buffer during hash absorption or squeeze operations. Because the state resides on the TEE kernel heap, adjacent heap metadata and neighboring allocations are corrupted whenever the vulnerable path executes.

Attack Vector

Exploitation requires local access with low privileges. A caller in the normal world or a compromised Trusted Application invokes SHA-3 operations that route through the vulnerable Crypto Extensions path. The off-by-one write occurs during standard hashing, so no crafted input beyond triggering the accelerated code path is required. The impact is limited to availability, but heap corruption within TEE kernel memory carries potential for further exploitation depending on the surrounding allocator layout.

No public proof-of-concept exploit is available for this vulnerability. See the OP-TEE Security Advisory GHSA-75x4-j8p9-55qv for technical details from the maintainers.

Detection Methods for CVE-2026-40257

Indicators of Compromise

Unexpected TEE kernel panics or crashes during or after SHA-3 hashing operations
Trusted Application failures returning TEE_ERROR_GENERIC or TEE_ERROR_OUT_OF_MEMORY from crypto calls
Secure world memory corruption traces visible in OP-TEE console logs on debug builds

Detection Strategies

Inspect OP-TEE build configuration for CFG_CRYPTO_WITH_CE82=y on ARMv8.2+ platforms running version 3.21.0 through 4.10.x
Audit firmware images and device manifests to identify deployed OP-TEE versions in fleet devices
Enable OP-TEE debug logging and heap canaries in test environments to observe corruption events triggered by SHA-3 workloads

Monitoring Recommendations

Track TEE service restarts and secure world abort messages in host kernel logs
Monitor Trusted Applications that rely on SHA-3 for signs of repeated crypto API failures
Correlate device stability telemetry with SHA-3 usage patterns from applications performing signature verification or attestation

How to Mitigate CVE-2026-40257

Immediate Actions Required

Upgrade OP-TEE to version 4.11.0 or later on all affected ARMv8.2+ devices
Identify all firmware images built with CFG_CRYPTO_WITH_CE82=y and prioritize them for patching
Restrict local access to devices running vulnerable OP-TEE builds until updates are deployed

Patch Information

OP-TEE version 4.11.0 contains the fix for CVE-2026-40257. The maintainers published details in OP-TEE Security Advisory GHSA-75x4-j8p9-55qv. Rebuild firmware images against the patched release and re-flash affected devices through the standard secure update process.

Workarounds

Disable the ARM Crypto Extensions SHA-3 acceleration by setting CFG_CRYPTO_WITH_CE82=n in the OP-TEE build configuration
Rebuild OP-TEE with the software SHA-3 implementation until version 4.11.0 can be deployed
Limit Trusted Applications permitted to invoke SHA-3 hashing where feasible

bash

# Configuration example - disable vulnerable CE-accelerated SHA-3 in OP-TEE build
make CFG_CRYPTO_WITH_CE82=n \
     PLATFORM=<your-platform> \
     CFG_ARM64_core=y

# Verify the setting in the generated configuration
grep CFG_CRYPTO_WITH_CE82 out/arm-plat-<platform>/conf.mk