CVE-2026-53366: 
Linux Kernel vulnerability analysis and mitigation

CVE-2026-53366 is a memory allocation accounting error in the Linux kernel's IPv4 packet fragmentation handling code (__ip_append_data()) that can lead to memory corruption. The flaw was published on July 16, 2026, and affects Linux kernel versions 6.0 through multiple stable branches. Specifically, vulnerable ranges include 6.0–6.6.143, 6.7–6.12.94, 6.13–6.18.37, and 6.19–7.1.2. It carries a CVSS v3.1 base score of 7.8 (High) (GitHub Advisory, Red Hat).

The root cause is an incorrect calculation of buffer size (CWE-131) in the paged-allocation branch of __ip_append_data(). When this branch is taken, alloclen is set to fragheaderlen + transhdrlen and pagedlen to datalen - transhdrlen, but datalen already includes fraggap bytes that are subsequently copied into the new socket buffer's linear area via skb_copy_and_csum_bits(). This causes the linear area to be undersized by fraggap bytes while pagedlen is overstated by the same amount — a mismatch absent in the non-paged branch, which correctly uses fraglen (which accounts for fraggap). The fix adds fraggap to alloclen and subtracts it from pagedlen in the paged path. Exploitation requires local access with network socket privileges and the ability to craft IPv4 packets that trigger the fragmentation path (GitHub Advisory, Red Hat Bugzilla).

Successful exploitation by a local user with network socket privileges could result in memory corruption within the kernel's socket buffer handling, potentially enabling arbitrary code execution or denial of service. All three security dimensions are affected: confidentiality, integrity, and availability are each rated High in the CVSS scoring. The vulnerability is confined to the local system (scope unchanged), but kernel-level code execution could allow privilege escalation and full system compromise (GitHub Advisory, Red Hat).

Apply the appropriate kernel update for your branch: 6.6.144 or later (for 6.0–6.6.x), 6.12.95 or later (for 6.7–6.12.x), 6.18.38 or later (for 6.13–6.18.x), or 7.1.3 or later (for 6.19+). Upstream fixes are available in the stable kernel tree (kernel.org patch 1, kernel.org patch 2). Distribution-specific updates have been released by Red Hat, SUSE (SUSE-SU-2026:3130-1, SUSE-SU-2026:3156-1, SUSE-SU-2026:3166-1), Debian (linux 6.1.177-1), and Ubuntu (SUSE Advisory, Red Hat). As a workaround where patching is not immediately possible, restrict local user access to raw and UDP network socket operations.

Red Hat triaged the vulnerability and assigned a CVSS v3.1 score of 7.8 (High), with the issue tracked in their Bugzilla (Red Hat Bugzilla). SUSE issued multiple security advisories and updates across their product lines shortly after disclosure. A security researcher published a technical blog post analyzing the vulnerability (qwerty blog), and the issue was discussed on the oss-security mailing list (oss-sec). The Yocto Project security list also flagged the issue for embedded Linux maintainers.