Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:HCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). EPSS scores by FIRST (EPSS SIG), generated by Empirical Security. Risk Priority is our own derived reading, not an NVD score.
Summary
CVE-2026-31608 is a critical-severity Double Free (CWE-415) vulnerability in Linux Kernel. Its CVSS base score is 9.8 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation of Remote Services (T1210); ranked at the 39th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SA-8 (Security and Privacy Engineering Principles) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-31608 is a double-free vulnerability (CWE-415) in the Linux kernel's SMB server component. The issue occurs because smb_direct_flush_send_list() already invokes smb_direct_free_sendmsg(), but the code erroneously calls it again after moving post_sendmsg() to the batch list, leading to a double-free condition. This affects Linux kernel versions prior to the application of the relevant stable patches.
A remote attacker with network access can exploit this vulnerability without privileges or user interaction, as indicated by its CVSS v3.1 base score of 9.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H). Successful exploitation could result in high-impact confidentiality, integrity, and availability violations, potentially enabling memory corruption, arbitrary code execution, or system crashes on affected SMB servers.
Mitigation is available through upstream Linux kernel patches in stable branches, as documented in the following commit references: https://git.kernel.org/stable/c/2ba03f46132b0d1a7bafb86e1ef61951a2254023, https://git.kernel.org/stable/c/6968c91fab05b8fc4d6700e0cf34472bb422df25, https://git.kernel.org/stable/c/830de6eeb9db4cb7e758201fb99328ef4ca4b032, and https://git.kernel.org/stable/c/84ff995ae826aa6bbcc6c7b9ea569ff67c021d72. Security practitioners should update to kernels incorporating these fixes and monitor for SMB server exposure on public networks.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-25501
Vulnerability Data
In the Linux kernel, the following vulnerability has been resolved: smb: server: avoid double-free in smb_direct_free_sendmsg after smb_direct_flush_send_list() smb_direct_flush_send_list() already calls smb_direct_free_sendmsg(), so we should not call it again after post_sendmsg() moved it to the batch list.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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- 1 hardening rule · 1 OS baseline
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Mitigating Controls (NIST 800-53 r5) AI
Developer testing and evaluation explicitly includes dynamic analysis and fuzzing that locate double-free defects before release.
Security engineering principles can require memory-safe allocation patterns or language features that structurally eliminate double-free opportunities.
Flaw remediation processes require identification and correction of memory-management defects such as double free once discovered.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Secure SDLC practices directly prevent double-free errors via static analysis, safe memory APIs, and testing.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Security testing in development can detect double-free conditions before release.
Secure coding standards directly address proper use of free() and similar functions.
Hardening callouts derived
Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over `controls_xwalks` (higher-evidence rows only; rows rated `none` are excluded).
Oracle Linux 8 (1 rule)
- V-248590 OL 8 must clear the page allocator to prevent use-after-free attacks. blocks CWE-415