Linux hwe edge: In the Linux kernel, the following vulnerability has been resolved: ksmbd: use check_add_overflow() to prevent u16 DACL size overflow… (CVE-2026-31704)
In the Linux kernel, the following vulnerability has been resolved: ksmbd: use check_add_overflow() to prevent u16 DACL size overflow set_posix_acl_entries_dacl() and set_ntacl_dacl() accumulate ACE sizes in u16 variables. When a file has many POSIX ACL entries, the accumulated size can wrap past 65535, causing the pointer arithmetic (char *)pndace + *size to land within already-written ACEs. Subsequent writes then overwrite earlier entries, and pndacl->size gets a truncated value. Use check_add_overflow() at each accumulation point to detect the wrap before it corrupts the buffer, consistent with existing check_mul_overflow() usage elsewhere in smbacl.c.
AI Analysis
Technical Summary
The Linux kernel ksmbd subsystem had a vulnerability (CVE-2026-31704) where the accumulation of Access Control Entry (ACE) sizes in 16-bit unsigned integers (u16) could overflow when a file has many POSIX ACL entries. This overflow causes pointer arithmetic to wrap around, resulting in writes overwriting earlier ACL entries and corrupting the buffer size field. The fix involved using check_add_overflow() at each accumulation point to detect and prevent this overflow, aligning with existing overflow checks in the smbacl.c code. This vulnerability affects Linux kernel versions prior to 6.8.0-1064.72~22.04.1 and other similar builds. The issue was addressed in the Linux kernel updates released by Ubuntu as part of their security notices USN-8488-1 and USN-8488-2. The CVSS v3.1 base score is 5.5 (medium severity), with local attack vector, low complexity, requiring low privileges, no user interaction, unchanged scope, no confidentiality or integrity impact, but high impact on availability.
Potential Impact
The vulnerability can cause buffer corruption in the ksmbd subsystem of the Linux kernel due to integer overflow in ACL size calculations. This corruption may lead to denial of service or system instability (availability impact). There is no reported impact on confidentiality or integrity. No known exploits are currently reported in the wild.
Mitigation Recommendations
A patch is available and has been released by Ubuntu in their Linux kernel updates (see Ubuntu Security Notices USN-8488-1 and USN-8488-2). Users should update their Linux kernel to versions 6.8.0 and later or the corresponding patched package versions provided by their distribution. After updating, a system reboot is required to apply the fixes. Due to an ABI change, recompilation and reinstallation of third-party kernel modules may be necessary. No additional mitigations are indicated by the vendor advisory.
Linux hwe edge: In the Linux kernel, the following vulnerability has been resolved: ksmbd: use check_add_overflow() to prevent u16 DACL size overflow… (CVE-2026-31704)
Description
In the Linux kernel, the following vulnerability has been resolved: ksmbd: use check_add_overflow() to prevent u16 DACL size overflow set_posix_acl_entries_dacl() and set_ntacl_dacl() accumulate ACE sizes in u16 variables. When a file has many POSIX ACL entries, the accumulated size can wrap past 65535, causing the pointer arithmetic (char *)pndace + *size to land within already-written ACEs. Subsequent writes then overwrite earlier entries, and pndacl->size gets a truncated value. Use check_add_overflow() at each accumulation point to detect the wrap before it corrupts the buffer, consistent with existing check_mul_overflow() usage elsewhere in smbacl.c.
CVSS v3.1
Score 5.5medium
Affected software
pkg:deb/ubuntu/[email protected]~16.04.1?arch=source&distro=xenialpkg:deb/ubuntu/[email protected]?arch=source&distro=bionicpkg:deb/ubuntu/[email protected]?arch=source&distro=bionicpkg:deb/ubuntu/[email protected]?arch=source&distro=bionicpkg:deb/ubuntu/[email protected]?arch=source&distro=bionicpkg:deb/ubuntu/[email protected]~18.04.2?arch=source&distro=bionicpkg:deb/ubuntu/[email protected]?arch=source&distro=bionicpkg:deb/ubuntu/[email protected]~18.04.1?arch=source&distro=bionicpkg:deb/ubuntu/[email protected]?arch=source&distro=bionicpkg:deb/ubuntu/[email protected]~18.04.1?arch=source&distro=bionicpkg:deb/ubuntu/[email protected]~18.04.1?arch=source&distro=bionicpkg:deb/ubuntu/[email protected]?arch=source&distro=bionicpkg:deb/ubuntu/[email protected]~18.04.2?arch=source&distro=bionicpkg:deb/ubuntu/[email protected]?arch=source&distro=bionicpkg:deb/ubuntu/[email protected]?arch=source&distro=bionicpkg:deb/ubuntu/[email protected]~18.04.1?arch=source&distro=bionicpkg:deb/ubuntu/[email protected]~20.04.1?arch=source&distro=focalpkg:deb/ubuntu/[email protected]~20.04.1?arch=source&distro=focalpkg:deb/ubuntu/[email protected]~20.04.1?arch=source&distro=esm-infra/focalpkg:deb/ubuntu/[email protected]~20.04.1?arch=source&distro=focalpkg:deb/ubuntu/[email protected]~20.04.2?arch=source&distro=focalpkg:deb/ubuntu/[email protected]~20.04.1?arch=source&distro=focalpkg:deb/ubuntu/[email protected]~20.04.1?arch=source&distro=esm-infra/focalpkg:deb/ubuntu/[email protected]~20.04.1?arch=source&distro=focalpkg:deb/ubuntu/[email protected]+cvm1.1?arch=source&distro=focalpkg:deb/ubuntu/[email protected]~20.04.1?arch=source&distro=esm-infra/focalpkg:deb/ubuntu/[email protected]~20.04.3?arch=source&distro=focalpkg:deb/ubuntu/[email protected]~20.04.1?arch=source&distro=focalpkg:deb/ubuntu/[email protected]~20.04.1?arch=source&distro=esm-infra/focalpkg:deb/ubuntu/[email protected]?arch=source&distro=focalpkg:deb/ubuntu/[email protected]?arch=source&distro=focalpkg:deb/ubuntu/[email protected]~20.04.1?arch=source&distro=focalpkg:deb/ubuntu/[email protected]?arch=source&distro=focalpkg:deb/ubuntu/[email protected]~20.04.1?arch=source&distro=focalpkg:deb/ubuntu/[email protected]~20.04.1?arch=source&distro=focalpkg:deb/ubuntu/[email protected]~20.04.1?arch=source&distro=focalpkg:deb/ubuntu/[email protected]~20.04.1?arch=source&distro=esm-infra/focalpkg:deb/ubuntu/[email protected]~20.04.1?arch=source&distro=focalpkg:deb/ubuntu/[email protected]~20.04.1?arch=source&distro=esm-infra/focalpkg:deb/ubuntu/[email protected]?arch=source&distro=focalpkg:deb/ubuntu/[email protected]~20.04.1?arch=source&distro=esm-infra/focalpkg:deb/ubuntu/[email protected]~20.04.1?arch=source&distro=esm-infra/focalpkg:deb/ubuntu/[email protected]~20.04.1?arch=source&distro=esm-infra/focalpkg:deb/ubuntu/[email protected]?arch=source&distro=focalpkg:deb/ubuntu/[email 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protected]?arch=source&distro=questingpkg:deb/ubuntu/[email protected]?arch=source&distro=questingpkg:deb/ubuntu/[email protected]?arch=source&distro=questingpkg:deb/ubuntu/[email protected]?arch=source&distro=questingpkg:deb/ubuntu/[email protected]?arch=source&distro=questingpkg:deb/ubuntu/[email protected]?arch=source&distro=questingpkg:deb/ubuntu/[email protected]?arch=source&distro=questingpkg:deb/ubuntu/[email protected]?arch=source&distro=questingpkg:deb/ubuntu/[email protected]?arch=source&distro=questingpkg:deb/ubuntu/[email protected]?arch=source&distro=resolutepkg:deb/ubuntu/[email protected]?arch=source&distro=resolutepkg:deb/ubuntu/[email protected]?arch=source&distro=resolutepkg:deb/ubuntu/[email protected]?arch=source&distro=resolutepkg:deb/ubuntu/[email protected]?arch=source&distro=resolutepkg:deb/ubuntu/[email protected]?arch=source&distro=resolutepkg:deb/ubuntu/[email protected]?arch=source&distro=resolutepkg:deb/ubuntu/[email protected]?arch=source&distro=resolutepkg:deb/ubuntu/[email protected]?arch=source&distro=resolutepkg:deb/ubuntu/[email protected]?arch=source&distro=resolutepkg:deb/ubuntu/[email protected]?arch=source&distro=resoluteRun on your own infrastructure? 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AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The Linux kernel ksmbd subsystem had a vulnerability (CVE-2026-31704) where the accumulation of Access Control Entry (ACE) sizes in 16-bit unsigned integers (u16) could overflow when a file has many POSIX ACL entries. This overflow causes pointer arithmetic to wrap around, resulting in writes overwriting earlier ACL entries and corrupting the buffer size field. The fix involved using check_add_overflow() at each accumulation point to detect and prevent this overflow, aligning with existing overflow checks in the smbacl.c code. This vulnerability affects Linux kernel versions prior to 6.8.0-1064.72~22.04.1 and other similar builds. The issue was addressed in the Linux kernel updates released by Ubuntu as part of their security notices USN-8488-1 and USN-8488-2. The CVSS v3.1 base score is 5.5 (medium severity), with local attack vector, low complexity, requiring low privileges, no user interaction, unchanged scope, no confidentiality or integrity impact, but high impact on availability.
Potential Impact
The vulnerability can cause buffer corruption in the ksmbd subsystem of the Linux kernel due to integer overflow in ACL size calculations. This corruption may lead to denial of service or system instability (availability impact). There is no reported impact on confidentiality or integrity. No known exploits are currently reported in the wild.
Mitigation Recommendations
A patch is available and has been released by Ubuntu in their Linux kernel updates (see Ubuntu Security Notices USN-8488-1 and USN-8488-2). Users should update their Linux kernel to versions 6.8.0 and later or the corresponding patched package versions provided by their distribution. After updating, a system reboot is required to apply the fixes. Due to an ABI change, recompilation and reinstallation of third-party kernel modules may be necessary. No additional mitigations are indicated by the vendor advisory.
Technical Details
- Gcve Source
- db.gcve.eu
- Osv Id
- UBUNTU-CVE-2026-31704
- Osv Schema Version
- 1.7.0
- Ecosystems
- ["Ubuntu:16.04:LTS","Ubuntu:18.04:LTS","Ubuntu:20.04:LTS","Ubuntu:Pro:20.04:LTS","Ubuntu:22.04:LTS","Ubuntu:Nvidia-BlueField:22.04:LTS","Ubuntu:Pro:FIPS-preview:22.04:LTS","Ubuntu:Pro:FIPS-updates:22.04:LTS","Ubuntu:Pro:Realtime:22.04:LTS","Ubuntu:24.04:LTS","Ubuntu:Nvidia-BlueField:24.04:LTS","Ubuntu:Pro:FIPS-updates:24.04:LTS","Ubuntu:Pro:Realtime:24.04:LTS","Ubuntu:25.10","Ubuntu:26.04:LTS"]
- Cvss Version
- 3.1
Threat ID: 6a5b61b42d1edb114c88521c
Added to database: 07/18/2026, 11:21:24 UTC
Last enriched: 08/01/2026, 04:54:56 UTC
Last updated: 09/15/2026, 10:01:31 UTC
Views: 21
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