CVE-2026-43284
HighCVSS 8.8Exploitation Probability (EPSS)
Very high risk100th percentile - higher than 100% of all known CVEs
Summary
A vulnerability was found in the Linux kernel's ESP (Encapsulating Security Payload) implementation for IPv4/IPv6. The UDP datagram append paths did not mark shared pipe pages with the SKBFL_SHARED_FRAG flag, allowing in-place decryption without making a private copy. An attacker could exploit this to read or modify ESP data in UDP packets originating from shared pages.
Risk Assessment
The organization is at risk of potential leakage or modification of data transmitted through ESP-in-UDP tunnels, compromising the confidentiality and integrity of VPN/IPsec communication. The vulnerability can be exploited locally by a process with access to shared memory pages.
Recommendation
Immediately update the Linux kernel to a version containing the fix (commit 'xfrm: esp: avoid in-place decrypt on shared skb frags'). Monitor your distribution for the patch and apply it as a priority.
Original NVD description (English source)
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().