CVE-2026-40257: OP-TEE ARM SHA-3 Crypto Extensions Heap Overflow (CVSS 5.5)

Technical summary

The vulnerability resides in OP-TEE's ARM Crypto Extensions (CE) accelerated SHA-3 implementation, specifically affecting systems built with the CFG_CRYPTO_WITH_CE82=y configuration flag. An off-by-one error in buffer boundary calculations allows a heap overflow that corrupts memory immediately following the SHA-3 hash state structure. Because the TEE kernel manages cryptographic operations and sensitive data, unrestricted heap corruption in this context can compromise confidentiality and integrity of trusted services and their secrets. The issue was introduced in version 3.21.0 and resolved in 4.11.0.

Business impact

This vulnerability impacts the security posture of any system relying on OP-TEE for trusted execution, including IoT devices, enterprise ARM-based platforms, and mobile systems leveraging TrustZone. While the CVSS score reflects a local attack vector (requiring prior access to the system), successful exploitation leads to arbitrary memory corruption within the TEE, potentially exposing cryptographic keys, sensitive data, or enabling further privilege escalation within the trusted domain. Organizations deploying OP-TEE as a security boundary should treat this as a mandatory patch event.

Affected systems

OP-TEE versions 3.21.0 through 4.10.x running on ARMv8.2 or newer processors with SHA3 Crypto Extensions enabled (CFG_CRYPTO_WITH_CE82=y). This includes embedded systems, SoCs, and development boards using modern ARM architecture. Systems with older ARMv8.0/8.1 or those that disabled the CE82 configuration flag are unaffected.

Exploitability

The vulnerability requires local code execution with user-level privileges to trigger the SHA-3 accelerated code path. While not remotely exploitable by default, it can be weaponized by local processes or applications calling OP-TEE's cryptographic services. No public exploit code has been disclosed, and the CVSS assessment reflects the local-only attack surface (AV:L) and requirement for prior system access (PR:L).

Remediation

Upgrade OP-TEE to version 4.11.0 or later as the primary mitigation. For environments unable to patch immediately, disable ARM Crypto Extensions acceleration by setting CFG_CRYPTO_WITH_CE82=n during TEE build and redeploying. This workaround trades performance for security and should be temporary pending a patched deployment.

Patch guidance

Apply OP-TEE version 4.11.0 or any subsequent release. Verify the build configuration in your deployed TEE matches the patch level, as OP-TEE is typically integrated into SoC firmware or bootloader binaries rather than updated independently. Coordinate patching with your SoC vendor or platform maintainer to obtain updated firmware images, test in a staging environment, and plan a controlled rollout to production devices. Confirm post-deployment that CFG_CRYPTO_WITH_CE82=y remains enabled (unless intentionally disabled as a workaround) to validate the patch was correctly applied.

Detection guidance

Monitor for crashes or memory corruption events within the TEE kernel, which may manifest as unexpected resets or TEE service failures. Enable debug logging in OP-TEE if available in your deployment to capture heap corruption indicators. Audit your build configurations to identify systems running affected versions and CFG_CRYPTO_WITH_CE82=y. Network-level detection is not feasible given the local-only attack vector; focus on inventory and configuration baseline reviews.

Why prioritize this

Although CVSS 5.5 appears moderate, the integrity of the TEE as a security boundary is fundamental to overall system trust. Heap corruption in the TEE kernel can bypass cryptographic protections, expose key material, or enable privilege escalation to the secure world. Organizations should prioritize this upgrade because: (1) it affects the foundation of secure execution on ARM platforms, (2) the workaround introduces measurable performance penalties, and (3) patching requires coordinated firmware updates that may necessitate device downtime.

Risk score, explained

CVSS 3.1 score of 5.5 (MEDIUM) reflects a local attack vector (AV:L), low attack complexity (AC:L), and requirement for user-level privileges (PR:L), resulting in high availability impact (A:H) but no direct confidentiality or integrity rating in the base vector. However, this scoring does not fully capture the strategic importance of TEE integrity; in practice, heap corruption in the secure world often enables further attacks. Security teams should consider context-specific factors: the criticality of OP-TEE to their device security model, the installed base of affected hardware, and the feasibility of patching.

Frequently asked questions