Memory-safety, zeroization, and correctness fixes across agent, SFTP, terminal, FPKI, and transport

[aidangarske]

F-4582, F-2869, F-6268, F-4592, F-6693, F-1684, F-2082, F-6694, F-3881, F-5852, F-4795, F-3210, F-4583, F-3446,
F-1278, F-3453, F-6277, F-4794, F-4106, F-4105, F-4108, F-5900, F-6698, F-6703

[Copilot]

Pull request overview

This PR hardens wolfSSH against memory-safety issues, improves sensitive-data handling/zeroization, and tightens correctness checks across core protocol paths (agent/SFTP/transport) and user-facing tooling/examples.

Changes:

• Strengthens bounds checks and parsing correctness in core code paths (e.g., RealPath sizing, SFTP handle parsing, path cleaning, console escape parsing).
• Improves memory hygiene by zeroizing sensitive/large buffers before freeing and removing passphrase content from logs.
• Extends test coverage for error paths (e.g., RealPath failure case; new internal unit test for AEAD tag failure).

Reviewed changes

Copilot reviewed 17 out of 17 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
wolfssh/internal.h	Raises default GEXDH minimum size for stronger security defaults.
tests/unit.c	Adds internal unit test for AEAD tag verification failure path.
tests/api.c	Adds RealPath negative test for separator+segment NUL room edge case.
src/wolfterm.c	Fixes console escape parsing state handling and newline writes.
src/wolfsftp.c	Zeroizes SFTP GET/PUT state buffers on cleanup; improves handle-size validation; fixes Windows offset check.
src/ssh.c	Tightens RealPath bounds checks for separator and NUL handling.
src/log.c	Corrects compile-time macro guard for default logging callback.
src/internal.c	Fixes key material lifecycle (leak prevention/zeroization) and path cleaning correctness; zeroizes ML-KEM private data.
src/certman.c	Enforces FPKI-approved certificate signature algorithms.
src/agent.c	Removes passphrase contents from logs; fixes potential key blob over-read; tightens message size validation; simplifies worker flow; uses ForceZero.
examples/portfwd/portfwd.c	Prevents password buffer overflow by bounding copied password length.
examples/echoserver/echoserver.c	Updates read usage in global-request thread (currently introduces a failure).
examples/client/common.c	Prevents password buffer overflow by bounding copied password length.
examples/client/client.c	Fixes Windows stdout WriteFile length to match actual bytes read.
apps/wolfsshd/configuration.c	Fixes QNX include handling by using full path for lstat and validating snprintf result.
apps/wolfssh/wolfssh.c	Fixes Windows stdout WriteFile length; avoids NULL deref when building command string.
apps/wolfssh/common.c	Adds missing length guard before parsing pubkey type length field.

Comments suppressed due to low confidence (1)

examples/echoserver/echoserver.c:328

• wolfSSH_stream_read() rejects bufSz==0 and returns WS_BAD_ARGUMENT, but this code now checks the return value and will always treat it as a failure (even though the intent seems to just service inbound packets for the global-request reply). Use wolfSSH_worker() here, and treat WS_WANT_READ as non-fatal in non-blocking mode.

        ret = wolfSSH_stream_read(threadCtx->ssh, buf, 0);
        if (ret != WS_SUCCESS)
        {
            printf("wolfSSH_stream_read Failed.\n");
            wolfSSH_shutdown(threadCtx->ssh);
            return NULL;
        }

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