CVE-2026-53763: Trustedfirmware OP-TEE Integer Overflow

CVE-2026-53763 Overview

CVE-2026-53763 affects OP-TEE, a Trusted Execution Environment (TEE) that runs alongside a non-secure Linux kernel on Arm Cortex-A cores using TrustZone technology. The vulnerability stems from 32-bit integer overflows in the AES-GCM implementation within OP-TEE core. When more than 512 megabytes of payload or Additional Authenticated Data (AAD) are processed, the authentication tag is computed with incorrect bit-length values. This weakens the integrity guarantees of AES-GCM authenticated encryption. The issue affects versions 3.0.0 through 4.10.x, with version 4.11.0 containing the fix.

Critical Impact
A local, low-privileged actor can cause AES-GCM authentication tags to be computed incorrectly for payloads exceeding 512 MB, undermining message integrity in the Trusted Execution Environment.

Affected Products

TrustedFirmware OP-TEE versions 3.0.0 through 4.10.x
Arm Cortex-A systems relying on OP-TEE core AES-GCM operations
Trusted Applications (TAs) using OP-TEE cryptographic services for large AES-GCM operations

Discovery Timeline

2026-07-06 - CVE-2026-53763 published to NVD
2026-07-07 - Last updated in NVD database

Technical Details for CVE-2026-53763

Vulnerability Analysis

The vulnerability is an integer overflow ([CWE-190]) in OP-TEE core's AES-GCM implementation. AES-GCM (Galois/Counter Mode) requires the encoded bit-lengths of both the plaintext and the AAD to be included in the final authentication tag computation. OP-TEE tracks these lengths using 32-bit integer arithmetic. Multiplying byte counts by 8 to obtain bit counts overflows when the byte count exceeds 512 MB (approximately 2^29 bytes). Once the overflow occurs, the length field feeding into the GHASH computation no longer reflects the true message size. The resulting authentication tag is mathematically inconsistent with the RFC 5116 and NIST SP 800-38D specifications for GCM.

Root Cause

The root cause is the use of 32-bit width variables to hold bit-length counters inside the AES-GCM tag finalization path of OP-TEE core. Because 2^32 bits equals 512 MB, any single AES-GCM operation processing more than 512 MB of payload or AAD triggers wraparound during the byte-to-bit conversion. The patch in version 4.11.0 widens these counters to accommodate the specified GCM maximum message size.

Attack Vector

Exploitation requires local access with low privileges, consistent with a Trusted Application or non-secure world caller invoking OP-TEE cryptographic services. An actor able to submit AES-GCM operations larger than 512 MB can force the TEE to produce authentication tags that do not correctly bind the message length. This can lead to integrity confusion between parties that rely on OP-TEE-generated tags for verification. Confidentiality and availability are not directly affected.

No public proof-of-concept exploit exists for this issue. The vulnerability mechanism is documented in the OP-TEE GitHub Security Advisory GHSA-fcm8-vjhf-6vqh.

Detection Methods for CVE-2026-53763

Indicators of Compromise

OP-TEE core binaries reporting a version between 3.0.0 and 4.10.x in build metadata or tee-supplicant logs
Trusted Applications performing single AES-GCM operations on payloads or AAD larger than 512 MB
Authentication tag verification failures on the receiving side when large AES-GCM ciphertexts originate from a vulnerable OP-TEE instance

Detection Strategies

Inventory firmware and OP-TEE core versions across Arm Cortex-A fleets and flag any deployment older than 4.11.0
Audit Trusted Application source and manifests to identify AES-GCM usage patterns that may exceed the 512 MB threshold
Correlate application-layer GCM tag validation failures with the OP-TEE version running on the producing device

Monitoring Recommendations

Ingest OP-TEE build strings and firmware version telemetry into a centralized SIEM or data lake for continuous version tracking
Monitor cryptographic error rates from services that consume AES-GCM output produced by TEE-backed workloads
Alert on Trusted Applications that request AES-GCM contexts with unusually large input buffers

How to Mitigate CVE-2026-53763

Immediate Actions Required

Upgrade OP-TEE core to version 4.11.0 or later on all affected Arm Cortex-A devices
Identify Trusted Applications that perform AES-GCM operations on data exceeding 512 MB and refactor them to chunk data below that boundary until patching is complete
Revalidate any long-term data protected by AES-GCM tags generated on vulnerable OP-TEE versions

Patch Information

OP-TEE version 4.11.0 contains the fix. Details are published in the OP-TEE Security Advisory GHSA-fcm8-vjhf-6vqh. Downstream vendors that ship OP-TEE as part of board support packages or secure firmware images must rebuild and redistribute updated images.

Workarounds

No official workarounds are available according to the vendor advisory
As a defensive measure, constrain Trusted Applications to process AES-GCM payloads and AAD in segments smaller than 512 MB using higher-level protocol framing
Restrict access to OP-TEE cryptographic services to trusted callers to reduce the local attack surface pending patch deployment

bash

# Verify installed OP-TEE core version on target device
xtest --version
strings /path/to/tee.bin | grep -i "OP-TEE"