CVE-2026-71968: OP-TEE OS Use-After-Free Vulnerability

CVE-2026-71968 Overview

CVE-2026-71968 is a use-after-free vulnerability [CWE-362] in the OP-TEE OS Trusted Application (TA) loader. The flaw affects OP-TEE OS through version 4.10.0 and is fixed in commit 8794043. An attacker with the ability to load a signed Trusted Application can set the TA_FLAG_CONCURRENT flag in the user TA signed header, causing two concurrent sessions to operate on the same shared context without locking. The resulting corruption of the uctx->vm_info.regions list frees vm_region nodes still in use, producing a use-after-free in S-EL1 secure-world kernel memory.

Critical Impact
Memory corruption inside the S-EL1 secure-world kernel undermines the isolation guarantees of the Trusted Execution Environment and can lead to compromise of secure-world confidentiality and integrity.

Affected Products

OP-TEE OS versions up to and including 4.10.0
OP-TEE OS builds prior to commit 8794043c4065c26a2b8b1313794ba5ba5f06d296
Any downstream firmware or SoC platform integrating a vulnerable OP-TEE OS build

Discovery Timeline

2026-08-10 - CVE-2026-71968 published to NVD
2026-08-10 - Last updated in NVD database

Technical Details for CVE-2026-71968

Vulnerability Analysis

OP-TEE OS is an open-source Trusted Execution Environment kernel that runs in the Arm secure world (S-EL1). The TA loader accepts a signed header that carries flag bits controlling execution behavior. The TA_FLAG_CONCURRENT flag is intended for pseudo-TAs (built into the secure-world kernel), not for user TAs loaded from the normal world. The loader failed to reject this flag on user TAs, allowing an attacker who can load a signed user TA to opt into concurrent execution paths that were never designed for its context.

Root Cause

The root cause is a missing input validation check on the flags field of the user TA signed header. When TA_FLAG_CONCURRENT is asserted on a user TA, two sessions can enter the same shared context in parallel without the locking that user TAs rely on. Concurrent memref parameter mapping and unmapping mutates the uctx->vm_info.regions list from multiple threads, freeing vm_region nodes while other threads still reference them. This produces a classic race condition leading to use-after-free.

Attack Vector

Exploitation requires the ability to load a signed Trusted Application, meaning the attacker must control or possess a TA signed with a key trusted by the target device. From the normal world, the attacker triggers two concurrent sessions against the malicious TA and races memref parameter operations to corrupt secure-world kernel memory. Successful exploitation yields memory corruption at S-EL1, breaking the security boundary between normal-world and secure-world code.

// Patch: reject TA_FLAG_CONCURRENT for user TAs (core/kernel/ldelf_loader.c)
if (arg_bbuf->flags & ~TA_FLAGS_MASK)
    return TEE_ERROR_BAD_FORMAT;

/* TA_FLAG_CONCURRENT is for pseudo-TAs only */
if (arg_bbuf->flags & TA_FLAG_CONCURRENT)
    return TEE_ERROR_BAD_FORMAT;

to_user_ta_ctx(uctx->ts_ctx)->ta_ctx.flags = arg_bbuf->flags;

Source: OP-TEE OS commit 8794043

// Patch: reject TA_FLAG_CONCURRENT during ELF parsing (ldelf/ta_elf.c)
err(TEE_ERROR_BAD_FORMAT, "Invalid TA flags(s) %#"PRIx32,
    elf->head->flags & ~TA_FLAGS_MASK);

if (elf->head->flags & TA_FLAG_CONCURRENT)
    err(TEE_ERROR_BAD_FORMAT, "Invalid TA flags(s) %#"PRIx32,
        elf->head->flags & TA_FLAG_CONCURRENT);

*ta_flags = elf->head->flags;

Source: OP-TEE OS commit 8794043

Detection Methods for CVE-2026-71968

Indicators of Compromise

Unexpected secure-world panics, aborts, or reboots correlated with TA session creation from the normal world
Trusted Applications whose signed headers assert TA_FLAG_CONCURRENT on a user TA
Repeated concurrent invocations of the same TA session identifier issuing memref parameter operations from client processes

Detection Strategies

Statically inspect signed TA binaries and reject any user TA whose header flags include TA_FLAG_CONCURRENT before deployment
Enable OP-TEE debug logging on test devices and monitor for TEE_ERROR_BAD_FORMAT on TA load after applying the patch, which confirms the guard is engaged
Correlate normal-world tee-supplicant activity with secure-world crash telemetry to surface race-condition exploitation attempts

Monitoring Recommendations

Track OP-TEE OS build versions across device fleets and flag any deployment running a build older than commit 8794043
Monitor kernel logs for TEE driver errors, secure-world resets, and unexpected TA termination patterns
Audit which signing keys are trusted by production devices and restrict who can produce signed TAs

How to Mitigate CVE-2026-71968

Immediate Actions Required

Update OP-TEE OS to a build that includes commit 8794043c4065c26a2b8b1313794ba5ba5f06d296 and rebuild affected firmware images
Inventory all signed Trusted Applications in production and confirm none rely on TA_FLAG_CONCURRENT in user TA headers
Restrict TA signing key access to a minimum set of trusted operators to reduce the population of attackers able to meet the exploitation precondition

Patch Information

The fix is upstreamed in OP-TEE OS commit 8794043c4065c26a2b8b1313794ba5ba5f06d296, merged via OP-TEE pull request #7900. The patch adds explicit checks in core/kernel/ldelf_loader.c and ldelf/ta_elf.c to reject any user TA whose signed header sets TA_FLAG_CONCURRENT, returning TEE_ERROR_BAD_FORMAT. Additional context is available in the VulnCheck advisory.

Workarounds

Reject or refuse to sign user TAs whose header flags include TA_FLAG_CONCURRENT as a policy enforced at the build and signing pipeline
Where feasible, limit TA loading to an allowlist of hashes for known-good Trusted Applications until firmware is updated
Reduce the trusted signing key surface so that unsigned or third-party TAs cannot be loaded on production devices

bash

# Update OP-TEE OS source and confirm the fix is present
cd optee_os
git fetch origin
git checkout 8794043c4065c26a2b8b1313794ba5ba5f06d296
git log --oneline -1

# Rebuild secure-world firmware for the target platform
make PLATFORM=<your_platform> CFG_TEE_CORE_LOG_LEVEL=2