CVE-2026-53302: Linux Kernel EIP93 HMAC Setkey Null Pointer Dereference DoS

Technical summary

CVE-2026-53302 is a null pointer dereference in the eip93_hmac_setkey() function within the Linux kernel's EIP93 hardware crypto module. The function allocates a temporary ahash transform using crypto_alloc_ahash() with the CRYPTO_ALG_ASYNC mask to derive HMAC ipad/opad material. However, this is contradictory: the lookup specifies a driver-specific cra_driver_name (e.g., "sha256-eip93") while excluding async algorithms via the mask. Since EIP93 registers only async hash implementations under those names, the allocation consistently fails with -ENOENT. When invoked from the AEAD setkey path, the failure leaves the SA record partially initialized with zeroed digest fields. Subsequent crypto operations dereference ctx->flags from an uninitialized transform context, triggering a kernel panic. The fix removes the CRYPTO_ALG_ASYNC mask restriction, allowing the lookup to succeed. The existing crypto_wait_req() infrastructure already handles async completion correctly, making the mask unnecessary.

Business impact

This vulnerability affects Linux systems using the EIP93 hardware crypto accelerator, found primarily in embedded and ARM-based platforms. Systems attempting HMAC-based encryption operations (particularly AEAD ciphers) will experience kernel panics, causing immediate denial of service. For infrastructure relying on these systems for security services or data processing, unplanned downtime directly impacts availability and may disrupt cryptographic operations. Organizations using affected hardware should prioritize patching to restore stability, though the vulnerability requires local authenticated access, limiting the blast radius in typical remote-first deployments.

Affected systems

The Linux kernel, specifically versions and builds that include the EIP93 hardware cryptography driver module (crypto_hw_eip93). The vulnerability is most relevant to embedded systems, ARM-based devices, and specialized hardware platforms equipped with EIP93 crypto accelerators. Desktop and server systems without EIP93 hardware are not affected. The issue manifests when the EIP93 crypto module is loaded and HMAC or AEAD operations are attempted.

Exploitability

Exploitation requires local system access and authenticated user privileges (PR:L per CVSS vector). The attacker must be able to invoke cryptographic operations using HMAC or AEAD algorithms backed by the EIP93 driver. This is not a remote vulnerability. Once triggered, the impact is reliable and deterministic—the kernel panic occurs consistently during the vulnerable operation. There is no user interaction required beyond issuing the crypto operation itself.

Remediation

Apply kernel patches that remove the CRYPTO_ALG_ASYNC mask from the crypto_alloc_ahash() call in eip93_hmac_setkey(). This allows the algorithm lookup to succeed by not artificially restricting the search to synchronous implementations. The fix is minimal and preserves the existing async completion handling through crypto_wait_req(). Monitor vendor advisories for patched kernel versions targeting systems with EIP93 hardware support.

Patch guidance

Obtain and install the patched Linux kernel version from your distribution or device vendor that includes the fix for eip93_hmac_setkey(). Verify the patch commit addresses the CRYPTO_ALG_ASYNC mask removal in the EIP93 driver code. Test the patch in a non-production environment before rolling out broadly, particularly if your systems depend on hardware-accelerated cryptography. Reboot affected systems after applying the patch.

Detection guidance

Monitor kernel logs and system event logs for eip93_aead_handle_result panic messages or kernel oops traces referencing the EIP93 driver. These indicate exploitation or exposure. If your platform does not use EIP93 hardware acceleration (verify via kernel modules and device presence), this vulnerability does not apply. Check dmesg or journalctl for crashes related to crypto operations on affected hardware. Organizations can also audit systems to confirm whether the EIP93 crypto module is actually loaded and in use.

Why prioritize this

Although the CVSS base score is 5.5 (MEDIUM), prioritization depends on whether your infrastructure actually deploys EIP93 hardware accelerators. If you do, patch immediately because kernel panics cause direct availability impact. If you do not, this is a lower priority. The local-only attack requirement and need for authenticated access reduce the remote attack surface, but the reliable crash mechanism and impact on cryptographic service availability warrant timely remediation for affected deployments.

Risk score, explained

The CVSS 3.1 score of 5.5 reflects a local attack vector (AV:L), low complexity (AC:L), requirement for low privileges (PR:L), no user interaction (UI:N), and high availability impact (A:H) with no confidentiality or integrity impact. The score appropriately captures a local denial-of-service condition that requires authentication, not a remote code execution or data breach vector. Organizations using EIP93 should weight this as more severe due to cryptography service disruption; others can apply standard MEDIUM prioritization.

Frequently asked questions