Linux Kernel up to 6.12.35/6.15.4/6.16-rc3 __access_ok comparison

CVSS Meta Temp Score
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CTI Interest Score
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4.9$0-$5k0.00

Summaryinfo

A vulnerability categorized as problematic has been discovered in Linux Kernel up to 6.12.35/6.15.4/6.16-rc3. This affects the function __access_ok. The manipulation results in comparison. This vulnerability is reported as CVE-2025-38434. No exploit exists. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability classified as problematic has been found in Linux Kernel up to 6.12.35/6.15.4/6.16-rc3. Affected is the function __access_ok. The manipulation with an unknown input leads to a comparison vulnerability. CWE is classifying the issue as CWE-697. The product compares two entities in a security-relevant context, but the comparison is incorrect, which may lead to resultant weaknesses. The impact remains unknown. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: Revert "riscv: Define TASK_SIZE_MAX for __access_ok()" This reverts commit ad5643cf2f69 ("riscv: Define TASK_SIZE_MAX for __access_ok()"). This commit changes TASK_SIZE_MAX to be LONG_MAX to optimize access_ok(), because the previous TASK_SIZE_MAX (default to TASK_SIZE) requires some computation. The reasoning was that all user addresses are less than LONG_MAX, and all kernel addresses are greater than LONG_MAX. Therefore access_ok() can filter kernel addresses. Addresses between TASK_SIZE and LONG_MAX are not valid user addresses, but access_ok() let them pass. That was thought to be okay, because they are not valid addresses at hardware level. Unfortunately, one case is missed: get_user_pages_fast() happily accepts addresses between TASK_SIZE and LONG_MAX. futex(), for instance, uses get_user_pages_fast(). This causes the problem reported by Robert [1]. Therefore, revert this commit. TASK_SIZE_MAX is changed to the default: TASK_SIZE. This unfortunately reduces performance, because TASK_SIZE is more expensive to compute compared to LONG_MAX. But correctness first, we can think about optimization later, if required.

The advisory is available at git.kernel.org. This vulnerability is traded as CVE-2025-38434 since 04/16/2025. The exploitability is told to be difficult. Technical details are known, but there is no available exploit. The structure of the vulnerability defines a possible price range of USD $0-$5k at the moment (estimation calculated on 01/03/2026).

The vulnerability scanner Nessus provides a plugin with the ID 271193 (Ubuntu 24.04 LTS / 25.04 : Linux kernel (Azure) vulnerabilities (USN-7834-1)), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 6.12.36, 6.15.5 or 6.16-rc4 eliminates this vulnerability. Applying the patch fe30c30bf3bb68d4a4d8c7c814769857b5c973e6/f8b1898748dfeb4f9b67b6a6d661f354b9de3523/890ba5be6335dbbbc99af14ea007befb5f83f174 is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the databases at Tenable (271193) and CERT Bund (WID-SEC-2025-1653). If you want to get best quality of vulnerability data, you may have to visit VulDB.

Affected

  • Debian Linux
  • Amazon Linux 2
  • Red Hat Enterprise Linux
  • Ubuntu Linux
  • SUSE Linux
  • Oracle Linux
  • IBM QRadar SIEM
  • SUSE openSUSE
  • RESF Rocky Linux
  • Dell Avamar
  • Open Source Linux Kernel
  • Dell NetWorker
  • Dell Secure Connect Gateway

Productinfo

Type

Vendor

Name

Version

License

Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 5.0
VulDB Meta Temp Score: 4.9

VulDB Base Score: 4.6
VulDB Temp Score: 4.4
VulDB Vector: 🔒
VulDB Reliability: 🔍

NVD Base Score: 5.5
NVD Vector: 🔒

CVSSv2info

AVACAuCIA
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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Comparison
CWE: CWE-697
CAPEC: 🔒
ATT&CK: 🔒

Physical: Partially
Local: Yes
Remote: Partially

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Nessus ID: 271193
Nessus Name: Ubuntu 24.04 LTS / 25.04 : Linux kernel (Azure) vulnerabilities (USN-7834-1)

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Kernel 6.12.36/6.15.5/6.16-rc4
Patch: fe30c30bf3bb68d4a4d8c7c814769857b5c973e6/f8b1898748dfeb4f9b67b6a6d661f354b9de3523/890ba5be6335dbbbc99af14ea007befb5f83f174

Timelineinfo

04/16/2025 CVE reserved
07/25/2025 +100 days Advisory disclosed
07/25/2025 +0 days VulDB entry created
01/03/2026 +162 days VulDB entry last update

Sourcesinfo

Vendor: kernel.org

Advisory: git.kernel.org
Status: Confirmed

CVE: CVE-2025-38434 (🔒)
GCVE (CVE): GCVE-0-2025-38434
GCVE (VulDB): GCVE-100-317682
CERT Bund: WID-SEC-2025-1653 - Linux Kernel: Mehrere Schwachstellen

Entryinfo

Created: 07/25/2025 19:03
Updated: 01/03/2026 23:09
Changes: 07/25/2025 19:03 (57), 08/21/2025 05:14 (7), 09/15/2025 02:14 (1), 09/29/2025 00:24 (1), 10/26/2025 09:44 (2), 11/02/2025 13:03 (1), 11/17/2025 06:19 (1), 11/19/2025 21:06 (12), 01/03/2026 23:09 (1)
Complete: 🔍
Cache ID: 216::103

If you want to get best quality of vulnerability data, you may have to visit VulDB.

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