The skb that wasn't freed - the Fragnesia primitive via Open vSwitch
Doyensec details CVE-2026-90049 in Open vSwitch, enabling deterministic Linux kernel local privilege escalation on default major distribution installs.
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CVE-2026-43284
Linux kernel ESP-in-UDP decrypts in place over shared splice pages (CWE-123)
- CVSS 3.1
- 8.8 high
- EPSS
- 94%p100
- Published
- ·
- Modified
AI analysisSummaries by Vani AI
CVE-2026-43284 is a write-what-where memory-safety flaw (CWE-123) in the Linux kernel's xfrm/ESP (IPsec) code: the IPv4/IPv6 UDP datagram send paths fail to mark pages spliced into a UDP skb with SKBFL_SHARED_FRAG when MSG_SPLICE_PAGES attaches pipe pages, so the ESP input path wrongly treats the packet as privately owned and decrypts it in place over memory the skb does not exclusively own. It is triggered when locally generated UDP traffic built from spliced pipe pages is processed by the ESP decryption path, typically in IPsec NAT-traversal (ESP-in-UDP, UDP port 4500) configurations; the in-place decrypt can corrupt or expose data still referenced by the pipe or other owners of those shared pages. A local, low-privileged attacker can thereby cause high-severity confidentiality, integrity, and availability impact that extends beyond the packet itself (CVSS 3.1: 8.8, scope changed); no remote or unauthenticated trigger is described. Any Linux system running a kernel with the vulnerable UDP splice and ESP-in-UDP paths is affected, most importantly IPsec VPN gateways and clients; the advisory lists no affected version ranges. No public proof-of-concept or confirmed in-the-wild exploitation is known (not on CISA KEV), but EPSS assigns a 93.2% probability of exploitation within 30 days (100th percentile), so patching should not be deferred.
What to do: Apply your distribution's kernel security update containing the xfrm/esp fix for CVE-2026-43284 and reboot into the patched kernel, prioritizing IPsec VPN gateways and clients that use ESP-in-UDP NAT-T (UDP/4500). Until patched, restrict untrusted local users from sending splice-based (MSG_SPLICE_PAGES) UDP traffic through IPsec-protected paths, or temporarily avoid ESP-in-UDP encapsulation where feasible. Verify the fix via your vendor's package changelog, as the advisory does not name specific fixed version numbers.
| Product | Affected |
|---|---|
| Linux kernel | — |
Estimated exposure
mass≈1M+ Linux installations carry the vulnerable code in default distro kernels; hundreds of thousands of hosts expose IPsec NAT-T (UDP/4500) in public internet… — The xfrm/ESP and UDP datagram splice code ships in default distribution kernels and ESP-in-UDP NAT-T is the standard NAT-traversal mode for mainstream IPsec VPNs (on the order of 100k+ UDP/4500 endpoints visible in public scans), but only…
Order-of-magnitude estimate by the model from install counts, market share and public scan data it knows; verify before quoting.
Description · NVD
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().
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