# CVE-2026-52996: ksmbd: fix durable fd leak on ClientGUID mismatch in durable v2 open

CVE-2026-52996 is fixed in linux on 1 platform, first by DEBIAN-CVE-2026-52996, released June 25, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-52996
- Priority: High
- CVSS: 7.1 (Moderate)
- EPSS: 0.0017
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jun 24, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-52996

## Description

In the Linux kernel, the following vulnerability has been resolved:  ksmbd: fix durable fd leak on ClientGUID mismatch in durable v2 open  ksmbd_lookup_fd_cguid() returns a ksmbd_file with its refcount incremented via ksmbd_fp_get(). parse_durable_handle_context() in the DURABLE_REQ_V2 case properly releases this reference on every path inside the ClientGUID-match branch, either by calling ksmbd_put_durable_fd() or by transferring ownership to dh_info->fp for a successful reconnect. However, when an entry exists in the global file table with the same CreateGuid but a different ClientGUID, the code simply falls through to the new-open path without dropping the reference obtained from ksmbd_lookup_fd_cguid().  Per MS-SMB2 section 3.3.5.9.10 ("Handling the SMB2_CREATE_DURABLE_HANDLE_REQUEST_V2 Create Context"), the server MUST locate an Open whose Open.CreateGuid matches the request's CreateGuid AND whose Open.ClientGuid matches the ClientGuid of the connection that received the request. If no such Open is found, the server MUST continue with the normal open execution phase. A CreateGuid hit with a ClientGUID mismatch is therefore the "Open not found" case: proceeding with a new open is correct, but the reference obtained purely as a side effect of the lookup must not be leaked.  Repeated requests that hit this mismatch pin global_ft entries, prevent __ksmbd_close_fd() from ever running for the corresponding files, and defeat the durable scavenger, leading to long-lived resource leaks.  Release the reference in the mismatch path and clear dh_info->fp so subsequent logic does not mistake a non-matching lookup result for a reconnect target.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.12.94-1 | [DEBIAN-CVE-2026-52996](https://patchblox.com/security/data/fix/linux/debian-cve-2026-52996.md) | Jun 25, 2026 |
| Linux | linux Debian 14 | 7.0.10-1 | [DEBIAN-CVE-2026-52996](https://patchblox.com/security/data/fix/linux/debian-cve-2026-52996.md) | Jun 25, 2026 |

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Data as of 2026-11-09T01:18:40Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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