Always-Incorrect Control Flow Implementation in Linux kernel - CVE-2026-53393

Vulnerability identifier: #VU138870

CSH Severity: Medium

CVSS v4: 7.1 [CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-53393

CWE-ID: CWE-670

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote user to cause silent data loss.

The vulnerability exists due to improper state management in nfsd_vfs_write() and nfsd_commit() when handling deferred writeback errors for UNSTABLE write data followed by COMMIT. A remote user can trigger writeback errors and then issue COMMIT operations to cause silent data loss.

The issue violates the UNSTABLE+COMMIT durability contract by returning an unchanged write verifier after failed writeback.

Linux kernel
Ubuntu
linux (Ubuntu package)
linux-azure (Ubuntu package)
linux-gcp-7.0 (Ubuntu package)
linux-oracle-7.0 (Ubuntu package)
linux-oem-7.0 (Ubuntu package)
linux-azure-7.0 (Ubuntu package)

Install security update from vendor's repository.

Linux kernel - update to 7.0 rc3
linux (Ubuntu package) - addressed in versions 7.0.0-31.31, 7.0.0-31.31.1, 7.0.0-31.31~24.04.1, 7.0.0-1006.7, 7.0.0-1011.11~24.04.1, 7.0.0-1012.12, 7.0.0-1012.12~24.04.1
linux-azure (Ubuntu package) - addressed in versions 7.0.0-1011.11, 7.0.0-1014.14
linux-gcp-7.0 (Ubuntu package) - update to 7.0.0-1011.11~24.04.1
linux-oracle-7.0 (Ubuntu package) - update to 7.0.0-1011.11~24.04.1
linux-oem-7.0 (Ubuntu package) - update to 7.0.0-1013.13
linux-azure-7.0 (Ubuntu package) - update to 7.0.0-1014.14~24.04.1

• https://git.kernel.org/stable/c/1dd664b39774a9c89b72de8e59bf9ef4b3aaff2e
• https://git.kernel.org/stable/c/2090b05803faab8a9fa62fbff871007862cac1b7
• https://git.kernel.org/stable/c/4367afc119c51e17a616f6908772b7e2c2c4013f
• https://git.kernel.org/stable/c/b027cca33c97354149fcc0ddeede4525c41093cd

• Always-Incorrect Control Flow Implementation in Linux kernel nfsd
• Ubuntu update for linux-oem-7.0
• Ubuntu update for linux
• Ubuntu update for linux-gcp-7.0
• Ubuntu update for linux-oracle-7.0
• Ubuntu update for linux-azure
• Ubuntu update for linux-azure-7.0