CVE-2026-41515: OP-TEE RSA-OAEP Timing Side-Channel Padding Oracle

Technical summary

The vulnerability exists in OP-TEE's RSA-OAEP decryption path within the NXP CAAM crypto driver. During label hash verification, the implementation uses a non-constant-time `memcmp()` comparison instead of a constant-time variant. This, combined with multiple distinguishable error return paths in the decryption logic, creates a Manger-style padding oracle. An attacker capable of submitting crafted RSA-OAEP ciphertexts and observing decryption responses can extract plaintext via adaptive chosen ciphertext attacks—estimated at 1000–2000 queries to recover a single message. The constant-time comparison flaw is the root cause; the varied error paths amplify the information leakage. CWE-208 (Observable Timing Discrepancy) captures the core defect.

Business impact

The practical impact is limited by access constraints. An attacker must have local access to the OP-TEE environment and the ability to submit multiple decryption queries without detection. Compromised devices or insider threats pose the primary risk. For organizations using OP-TEE in high-security applications (secure boot, key management, trusted storage), this vulnerability could allow recovery of encrypted secrets if an attacker gains a foothold on the device. The low CVSS score reflects the requirement for local privilege and the large query count; however, for systems protecting cryptographic material, the recovery of encrypted data represents a significant confidentiality breach.

Affected systems

OP-TEE versions 3.9.0 through 4.10.x are affected. The flaw is specific to the NXP CAAM RSA driver component. Systems deployed on Arm Cortex-A processors with TrustZone and using the NXP CAAM accelerator for RSA-OAEP decryption are in scope. Organizations running OP-TEE in IoT devices, embedded Linux systems, or secure mobile environments should audit their version numbers. Systems using alternative RSA implementations or those with CFG_CRYPTO_DRV_RSA disabled are not affected.

Exploitability

Exploitation requires local system access and the ability to execute code within the OP-TEE environment or interact with it through a vulnerable application. The attack is not remotely exploitable. An attacker must submit a large number of adaptive chosen ciphertexts (estimated 1000–2000) and observe decryption responses to extract plaintext. The requirement for repeated interactions and local privilege access, combined with the silent nature of the oracle, makes opportunistic exploitation unlikely. Targeted attacks against specific encrypted values are feasible if an attacker has sufficient control and time. The vulnerability is not currently tracked in the CISA Known Exploited Vulnerabilities catalog.

Remediation

Upgrade OP-TEE to version 4.11.0 or later, which addresses the timing side-channel in the RSA-OAEP decryption implementation. For immediate mitigation on systems unable to patch promptly, disable the NXP CAAM RSA driver by setting CFG_CRYPTO_DRV_RSA=n during OP-TEE compilation; this falls back to software RSA implementations. Verify that your OP-TEE build configuration specifies the NXP CAAM driver before applying the workaround, as systems using alternative crypto drivers are not vulnerable.

Patch guidance

Patched version is OP-TEE 4.11.0. Organizations should verify this version number against the official Trusted Firmware project release notes and obtain the update from the canonical OP-TEE repository. If you are building OP-TEE from source, ensure you are pulling from a trusted branch post-4.11.0. If using a vendor distribution of OP-TEE (e.g., bundled with an SoC SDK), confirm with your vendor that their OP-TEE component includes the RSA-OAEP constant-time fix. Testing in a non-production environment is recommended given that OP-TEE updates can affect boot and cryptographic operations.

Detection guidance

Detection is challenging because the attack is passive from the target's perspective—it relies on observing decryption response behavior rather than system errors. Monitor for unusual patterns of RSA-OAEP decryption requests from untrusted local processes or applications, particularly those submitting high volumes of invalid ciphertexts. Enable cryptographic operation logging if available in your OP-TEE configuration. Review OP-TEE version numbers across your device fleet using inventory or MDM tools. If you suspect exploitation, correlate device behavior logs with periods of local privilege escalation or suspicious application activity. Performance testing may reveal statistical anomalies in decryption latencies if an attacker is systematically probing the oracle.

Why prioritize this

While the CVSS score is low (2.5), this is a cryptographic side-channel against a trusted execution environment—a domain where even theoretical vulnerabilities merit attention. The attack requires local access and many queries, limiting blast radius. However, if your organization relies on OP-TEE to protect sensitive encryption keys or sealed data, the potential recovery of plaintext represents a material confidentiality loss. Prioritize patching for systems in high-security deployments (secure enclaves, key management appliances, sealed device configs). For general IoT and embedded Linux deployments using OP-TEE for less critical functions, plan patching within a normal update cycle. The absence of active exploitation in the wild and the low CVSS should not delay remediation in cryptographically sensitive contexts.

Risk score, explained

The CVSS 3.1 score of 2.5 (LOW) reflects the local-access requirement (AV:L), high attack complexity due to the need for adaptive queries and observation (AC:H), and low privilege level (PR:L). Confidentiality impact is rated (C:L) because plaintext recovery is theoretically possible but requires substantial effort. Integrity and availability are unaffected (I:N/A:N). This scoring appropriately captures the exploit barrier but may underweight the cryptographic sensitivity for certain deployments. Security teams should treat this as a medium-priority patch for systems where RSA-OAEP ciphertexts protect high-value secrets, and as standard-priority for general-purpose OP-TEE deployments.

Frequently asked questions