HIGH
Dirty Frag
CVE-2026-43284
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
KernelScan AI7.8HIGH
01Description
In the Linux kernel, the following vulnerability has been resolved: xfrm: esp: avoid in-place decrypt on shared skb frags MSG_SPLICE_PAGES can attach pages from a pipe directly to an skb. TCP marks such skbs with SKBFL_SHARED_FRAG after skb_splice_from_iter(), so later paths that may modify packet data can first make a private copy. The IPv4/IPv6 datagram append paths did not set this flag when splicing pages into UDP skbs. That leaves an ESP-in-UDP packet made from shared pipe pages looking like an ordinary uncloned nonlinear skb. ESP input then takes the no-COW fast path for uncloned skbs without a frag_list and decrypts in place over data that is not owned privately by the skb. Mark IPv4/IPv6 datagram splice frags with SKBFL_SHARED_FRAG, matching TCP. Also make ESP input fall back to skb_cow_data() when the flag is present, so ESP does not decrypt externally backed frags in place. Private nonlinear skb frags still use the existing fast path. This intentionally does not change ESP output. In esp_output_head(), the path that appends the ESP trailer to existing skb tailroom without calling skb_cow_data() is not reachable for nonlinear skbs: skb_tailroom() returns zero when skb->data_len is nonzero, while ESP tailen is positive. Thus ESP output will either use the separate destination-frag path or fall back to skb_cow_data().
02KernelScan AI Analysis
Risk summary
A local unprivileged attacker can exploit this vulnerability to overwrite setuid binaries or sensitive files, gaining root privileges. The exploit is public and works on all major distributions. Immediate action is required to mitigate by unloading the esp4, esp6 kernel modules until patches are applied.
Vulnerability analysis
Summary: A vulnerability in the Linux kernel's XFRM ESP fragment reassembly allows a local attacker to corrupt page-cache pages of files by causing the ESP decryption engine to write attacker-controlled plaintext directly into those pages, enabling root privilege escalation.
Root Cause: When processing ESP fragments, the kernel's XFRM input path does not validate that the destination buffer pages are safe to modify. An attacker can install a crafted SA with a high replay sequence number (seq_hi) encoding the desired plaintext. By splicing file data into a UDP socket and then sending a crafted ESP-encapsulated packet, the page-cache pages from the file become the reassembly buffer, and decryption overwrites them with attacker-controlled data.
Attack Surface: Local attacker with the ability to create user namespaces (default on most distributions) can exploit this. Inside a new user+network namespace, CAP_NET_ADMIN is obtained to install XFRM states; no other special privileges are required.
Fix Mechanism: The fix (commit f4c50a4034e62ab75f1d5cdd191dd5f9c77fdff4 in netdev) likely introduces checks to prevent the ESP reassembly from using page-cache pages as buffers, or ensures that decryption does not write into shared pages.
03Fix Versions
| Branch | Fixed in | Patch commit |
|---|---|---|
| 5.10 | 5.10.255 | a6cb440f274a |
| 5.15 | 5.15.206 | ab8b995323e5 |
| 6.1 | 6.1.172 | fe785bb3a809 |
| 6.12 | 6.12.87 | 8253aab4659c |
| 6.18 | 6.18.28 | 50ed1e787310 |
| 6.6 | 6.6.138 | 5d55c7336f80 |
| 7.0 | 7.0.5 | b54edf1e9a3f |
| mainline | 7.1-rc3 | 71a1d9d985d2 |