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The vulnerability resides in the F2FS filesystem’s sysfs interface, where attributes are exposed under `/sys/fs/f2fs/` for runtime tuning. The core issue is that the helper functions `__sbi_store()` (for writing) and `f2fs_sbi_show()` (for reading) incorrectly assume that all underlying data fields are of type `unsigned int` (4 bytes). This assumption leads to two critical memory safety problems. First, for attributes backed by smaller data types, such as the 8-bit `carve_out` field, writing a large value like `65537` causes an out-of-bounds write, corrupting adjacent kernel memory. Second, for attributes backed by larger data types, such as the 64-bit atgc_age_threshold, the interface truncates values larger than UINT_MAX. For instance, writing `4294967297` results in the value `1` being stored, as only the lower 32 bits are kept. The root cause is a lack of type awareness in the sysfs handlers, which the patch resolves by introducing a `size` field in `struct f2fs_attr` to ensure read/write operations use the correct data width, preventing both corruption and truncation .
dailycve form:
Platform: Linux Kernel
Version: Various
Vulnerability: Out-of-bounds write
Severity: Medium-High
date: March 4, 2026
Prediction: Patched mid-March
What Undercode Say:
Analytics:
The vulnerability has been publicly disclosed and patched in the mainline Linux kernel. The fix, which introduces a size-aware attribute handling mechanism, has been backported to various stable kernel branches. Linux distributions are in the process of releasing updated kernel packages. The vulnerability is local, requiring write access to F2FS sysfs attributes, which typically necessitates root privileges. However, it poses a significant risk in containerized environments or misconfigured systems where unprivileged processes might have such access .
Bash Commands and Codes:
Check if F2FS is in use and identify sysfs entries ls /sys/fs/f2fs/ Check current kernel version uname -r Restrict access to F2FS sysfs attributes as a temporary mitigation chmod 700 /sys/fs/f2fs// Monitor for exploitation attempts using auditd auditctl -w /sys/fs/f2fs/ -p wa -k f2fs_sysfs_access Search kernel logs for f2fs-related errors or crashes dmesg | grep -i f2fs journalctl -k | grep -i f2fs Example of vulnerable write (Do NOT run on production systems) echo 65537 > /sys/fs/f2fs/vde/carve_out Expected in a patched kernel: write error or value capped at 255
Exploit:
Exploitation involves a local attacker writing specially crafted large integer values to specific F2FS sysfs files. By targeting an attribute mapped to a small kernel variable (like carve_out), the attacker can trigger an out-of-bounds write. This memory corruption can be leveraged to crash the system (denial of service) or, with careful memory layout manipulation, potentially achieve local privilege escalation by overwriting adjacent kernel pointers or control data .
Protection from this CVE:
- Apply Patches: The primary and most effective protection is to update the Linux kernel to a version that includes the fix. This involves installing the latest security updates from your Linux distribution.
- Restrict Access: As a workaround, restrict write permissions to the `/sys/fs/f2fs/` directory tree, ensuring only privileged users (typically root) can modify these attributes.
- Strengthen Isolation: In containerized environments, avoid mounting the host’s sysfs filesystem into containers, especially with write permissions. Use mandatory access control systems like SELinux or AppArmor to create policies that deny unauthorized processes from writing to these sysfs nodes .
Impact:
Successful exploitation can lead to kernel memory corruption. This can result in a system crash (denial of service), unpredictable behavior of the F2FS filesystem, data corruption, or in the worst-case scenario, local privilege escalation where an attacker gains higher-level system privileges .
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Sources:
Reported By: nvd.nist.gov
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