Vulnerability record · CVE-2026-43284 · published 8 May 2026
CVE-2026-43284: Linux kernel ESP-in-UDP in-place decrypt on shared skb frags
Linux · Linux Kernel
The Linux kernel's IPv4/IPv6 datagram splice paths fail to mark skbs built from shared pipe pages with SKBFL_SHARED_FRAG, so ESP-in-UDP input treats them as ordinary uncloned nonlinear skbs and decrypts in place over memory the skb does not privately own. This is a local privilege escalation class flaw (CWE-123) in the kernel's xfrm/ESP handling. It matters because it allows corruption of externally backed page data reachable from a local context.
Description
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().
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
Automated analysis
high priorityCVSS 8.8 with high EPSS and public detection/mitigation scripts, but exploitation requires local low-privileged access and no KEV listing or known ransomware use.
What it is
The Linux kernel's IPv4/IPv6 datagram splice paths fail to mark skbs built from shared pipe pages with SKBFL_SHARED_FRAG, so ESP-in-UDP input treats them as ordinary uncloned nonlinear skbs and decrypts in place over memory the skb does not privately own. This is a local privilege escalation class flaw (CWE-123) in the kernel's xfrm/ESP handling. It matters because it allows corruption of externally backed page data reachable from a local context.
Impact
An attacker gains the ability to write decrypted data into pages not owned by the skb, enabling memory corruption that can lead to local privilege escalation. The CVSS vector rates confidentiality, integrity and availability impact as high with scope change.
Attack surface
Reached locally by a user able to trigger the IPv4/IPv6 datagram splice path and ESP-in-UDP processing; the CVSS vector is AV:L/PR:L/UI:N, so low privileges are required and no user interaction is needed. No remote or unauthenticated path is described.
Exploitation
Not listed in CISA KEV and no ransomware usage is documented, but EPSS is very high (0.93235, 99.83rd percentile) and public detection and mitigation scripts exist, indicating active interest. Reference tags are patch and mailing list only; no exploit tag is present.
What to do
- Apply the upstream stable kernel patches referenced in the git.kernel.org commit links and the Red Hat errata (RHSA-2026:16061 and related) as soon as possible.
- If patching cannot be immediate, restrict local access to untrusted users and reduce exposure of ESP-in-UDP services on affected hosts.
- Track vendor advisories for your distribution to confirm the fixed kernel version for your platform.
- Reboot or live-patch after applying the kernel update so the fix is active.
- Monitor for the public mitigation script referenced by Vicarius and validate it against your environment before relying on it.
Detection
- Monitor kernel logs for ESP/xfrm decryption errors or memory corruption warnings on hosts running ESP-in-UDP.
- Watch for local privilege escalation attempts or unusual processes gaining root on systems with IPsec/ESP-in-UDP enabled.
- Use the Vicarius detection script referenced in the advisory to check kernel version and configuration exposure.
- Audit which hosts run ESP-in-UDP and prioritize those for patch verification.
This assessment is produced automatically and is not human-reviewed. Verify against the vendor advisory before acting on it.
Affected products
1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.
References
Track CVE-2026-43284 inside VULONE
Watch it alongside the ransomware crews, C2 infrastructure and forum chatter that reference it, query it through the API and pull it into your SIEM over TAXII.
Related vulnerabilities
Same products first, then exploited flaws of the same weakness class.
Source: NIST National Vulnerability Database (record CVE-2026-43284), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.
