fix(dh): wipe DH private key from stack

[MarkAtwood]

Bug

In wolfCLU_DhParamSetup (src/dh/clu_dh.c), the genKey block declares a stack buffer byte priv[WOLFSSL_MAX_DH_BITS/8] and fills it with the DH private key via wc_DhGenerateKeyPair. When the block ends the function returns with priv left un-wiped on the stack, leaking private key material.

This is the outlier in wolfCLU's own convention: private-key buffers are scrubbed with wolfCLU_ForceZero throughout the codebase (clu_genkey.c, clu_sign.c, clu_pkcs8/pkcs12, etc.). The DH keygen path omitted the wipe.

Fix

Add wolfCLU_ForceZero(priv, sizeof(priv)) immediately before the block closes, after the outBuf free. wolfCLU_ForceZero is already declared in wolfclu/clu_header_main.h — no new include.

How verified

Compiled the patched translation unit against a wolfSSL --enable-all install (gcc -c, EXIT=0). Preprocessor + nm confirm the wolfCLU_ForceZero(priv, ...) call is live (undefined reference in the object, one call in the preprocessed output), not compiled out behind an ifdef.

Reported by static analysis (Fenrir finding 664).

[Copilot]

Pull request overview

Note

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Fixes a security bug in the DH parameter/key generation path where DH private key material was left resident on the stack after wolfCLU_DhParamSetup returns.

Changes:

• Scrub the stack-resident DH private key buffer (priv) via wolfCLU_ForceZero(priv, sizeof(priv)) before exiting the genKey block.

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