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Mallory
Medium

Timing side-channel in OpenSSL SM2 on 64-bit ARM

IdentifiersCVE-2025-9231CWE-208

CVE-2025-9231 is a timing side-channel vulnerability in OpenSSL's SM2 algorithm implementation affecting 64-bit ARM platforms. The issue occurs during SM2 signature computations and stems from non-constant-time behavior in the implementation, with the provided context specifically indicating that the fix addressed timing leakage in the modular inversion path in crypto/ec/ecp_sm2p256.c, including get_affine, field_inv, and inv_mod_ord. OpenSSL assessed that the timing signal could potentially permit private key recovery. OpenSSL does not directly support certificates with SM2 keys in TLS by default, so exposure is limited in most standard TLS deployments, but custom providers can enable such usage and make the issue relevant remotely. The FIPS modules for OpenSSL 3.5, 3.4, 3.3, 3.2, 3.1, and 3.0 are not affected because SM2 is not an approved algorithm there.

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ANALYST BRIEF

Impact, mitigation & remediation

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Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation could allow an attacker to recover an SM2 private key by analyzing timing differences in SM2 signature operations on affected 64-bit ARM systems. This would compromise the confidentiality and authenticity guarantees of the key, enabling signature forgery and any other operations dependent on possession of that private key. OpenSSL characterized remote key recovery as plausible based on observed timing signals, although the reporter did not demonstrate full remote key recovery over a network. The issue is therefore moderate severity and primarily relevant where SM2 private key operations are exposed in reachable application flows, especially via custom provider-based TLS or other remote cryptographic services.

Mitigation

If you can’t patch tonight, do this now.

If immediate patching is not possible, avoid or disable SM2 usage on affected 64-bit ARM systems, particularly for remotely reachable signing or private-key operations. Do not enable SM2 certificates in TLS through custom providers on affected platforms unless patched. Prefer deployments where SM2 private key operations are not exposed to remote timing observation. Where feasible, move affected workloads to non-affected builds or architectures, and restrict network access to services performing SM2 operations until updates are applied.

Remediation

Patch, then assume compromise.

Upgrade to a fixed OpenSSL release for the affected branch. The context indicates fixes were shipped in OpenSSL 3.5.4, 3.4.3, 3.3.5, and 3.2.6. Downstream vendors such as FreeBSD and Linux distributions also issued corresponding updates. Apply the vendor patch set that corrects the timing leakage in the SM2 implementation on 64-bit ARM, then restart or rebuild dependent services as needed so they link against the corrected library. FIPS modules do not require remediation for this issue because they are not affected.
PUBLIC EXPLOITS

Exploits

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VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

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VendorProductType
FreebsdFreebsdapplication
OpenSSL Software FoundationOpensslapplication

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Detection signatures

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