CVE-2026-72044

Description

In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix stack buffer overflow in multichannel session-key copy Commit 4b706360ffb7 ("ksmbd: fix multichannel binding and enforce channel limit") moved the binding-path session key out of the session-wide sess->sess_key (CIFS_KEY_SIZE = 40) into a new per-channel buffer, and sized both that buffer and the on-stack copy used during binding with SMB2_NTLMV2_SESSKEY_SIZE (16): struct channel { char sess_key[SMB2_NTLMV2_SESSKEY_SIZE]; /* 16 */ ... }; ntlm_authenticate() / krb5_authenticate(): char channel_key[SMB2_NTLMV2_SESSKEY_SIZE] = {}; /* 16 */ char *auth_key = conn->binding ? channel_key : sess->sess_key; The two writers that fill this destination still bound the copy length against CIFS_KEY_SIZE (40), not against the 16-byte buffer: ksmbd_decode_ntlmssp_auth_blob() (NTLM key exchange): if (sess_key_len > CIFS_KEY_SIZE) /* 40 */ return -EINVAL; arc4_crypt(ctx_arc4, sess_key, (char *)authblob + sess_key_off, sess_key_len); ksmbd_krb5_authenticate(): if (resp->session_key_len > sizeof(sess->sess_key)) /* 40 */ ... memcpy(sess_key, resp->payload, resp->session_key_len); On a binding SESSION_SETUP, auth_key points at the 16-byte channel_key, so a client that supplies an NTLM EncryptedRandomSessionKey of up to 40 bytes (with NTLMSSP_NEGOTIATE_KEY_EXCH), or a Kerberos ticket whose session key is longer than 16 bytes (a normal AES256 key is 32), writes past the 16-byte stack buffer -- up to a 24-byte kernel stack overflow. KASAN reports it as a stack-out-of-bounds write in arc4_crypt() called from ksmbd_decode_ntlmssp_auth_blob(). The destinations must be able to hold the full session key the length checks already permit. Size the per-channel key buffer and the two on-stack channel_key buffers with CIFS_KEY_SIZE, matching sess->sess_key.

Predictions

Heuristic predictions, AS-IS, for prioritization only.

Mitigations

References

• https://git.kernel.org/stable/c/610346149d047a52a92c9a0eb329dd565b8f92c5
• https://git.kernel.org/stable/c/9a7f7b55d7d0fbc4662c981ee6c56e081fa66d58