# CVE-2026-99083: ksmbd: fix heap out-of-bounds write in krb5_authenticate()

CVE-2026-99083 is fixed in linux on 1 platform, first by DEBIAN-CVE-2026-99083, released October 27, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-99083
- Priority: High
- CVSS: 8.8 (Important)
- EPSS: 0.0045
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Oct 23, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-99083

## Description

In the Linux kernel, the following vulnerability has been resolved:  ksmbd: fix heap out-of-bounds write in krb5_authenticate()  In krb5_authenticate(), out_len is calculated to determine available headroom in response_buf for the incoming Kerberos AP-REP token. However, when SMB2_SESSION_SETUP is processed as a non-first element of a compounded SMB2 request, the calculation omits work->next_smb2_rsp_hdr_off.  This causes out_len to overstate remaining buffer headroom by the cumulative size of prior responses in the compound chain. Consequently, the length check in ksmbd_krb5_authenticate() (*out_len <= resp->spnego_blob_len) passes erroneously, allowing memcpy() to write the AP-REP blob past the end of response_buf into adjacent kernel heap memory.  Fix this by subtracting work->next_smb2_rsp_hdr_off when computing out_len, ensuring it accurately reflects physical remaining buffer space.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.12.115-2 | [DEBIAN-CVE-2026-99083](https://patchblox.com/security/data/fix/linux/debian-cve-2026-99083.md) | Oct 27, 2026 |
| Linux | linux Debian 14 | 7.2.12-1 | [DEBIAN-CVE-2026-99083](https://patchblox.com/security/data/fix/linux/debian-cve-2026-99083.md) | Oct 27, 2026 |

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Data as of 2026-11-08T06:59:42Z 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 Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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