Linux Kernel up to 7.2-rc2 ksmbd ksmbd_decode_ntlmssp_auth_blob stack-based overflow

Summaryinfo

A vulnerability was found in Linux Kernel up to 7.2-rc2. It has been classified as very critical. Affected by this vulnerability is the function ksmbd_decode_ntlmssp_auth_blob of the component ksmbd. Performing a manipulation results in stack-based overflow. This vulnerability was named CVE-2026-72044. The attack may be initiated remotely. There is no available exploit.

Detailsinfo

A vulnerability, which was classified as very critical, was found in Linux Kernel up to 7.2-rc2. This affects the function ksmbd_decode_ntlmssp_auth_blob of the component ksmbd. The manipulation with an unknown input leads to a stack-based overflow vulnerability. CWE is classifying the issue as CWE-121. A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function). This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

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.

It is possible to read the advisory at git.kernel.org. This vulnerability is uniquely identified as CVE-2026-72044 since 08/09/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. Technical details of the vulnerability are known, but there is no available exploit. The pricing for an exploit might be around USD $5k-$25k at the moment (estimation calculated on 08/15/2026).

Upgrading to version 7.2-rc3 or 7.2-rc4 eliminates this vulnerability. Applying the patch 9a7f7b55d7d0fbc4662c981ee6c56e081fa66d58/610346149d047a52a92c9a0eb329dd565b8f92c5 is able to eliminate this problem.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 7.2-rc1
• 7.2-rc2

License

• open-source

Website

• Vendor: https://www.kernel.org/

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