AS-2026-008: Linux Kernel (Dirty Frag)

2026-05-12

Statement

A local privilege escalation (LPE) vulnerability, commonly known as "Dirty Frag", has been disclosed to affect the Linux kernel. If the vulnerability is exploited, an authenticated local user with standard privileges to bypass security restrictions and gain elevated system (root) permissions.

1. CVE-2026-43284 affects some ASUSTOR products with VPN Server is installed from the App Central and Linux Kernel versions higher than 4.11, from ADM 4.1 to ADM 5.1. Updates with Linux Kernel Patch in VPN Server will be released as soon as possible.
2. None of ASUSTOR's products are affected by CVE-2026-43500 as rxrpc is not used in ASUSTOR products.

Affected Products

NOT affected NAS models:

• Drivestor (AS1102T, AS1104T)
• Drivestor Pro (AS3302T, AS3304T)
• AS4002T, AS4004T

Mitigation

For NAS models with VPN server installed on ADM 4.1 to ADM 5.1, please disable or remove VPN server app before the upgraded app is available.

Detail

• CVE-2026-43284
  • Severity: High
  • CVSS3.1 Base Score: 8.8
  • CVSS3.1 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
  • 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().
• CVE-2026-43500
  • Severity: High
  • CVSS3.1 Base Score: 7.8
  • CVSS3.1 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  • In the Linux kernel, the following vulnerability has been resolved: rxrpc: Also unshare DATA/RESPONSE packets when paged frags are present The DATA-packet handler in rxrpc_input_call_event() and the RESPONSE handler in rxrpc_verify_response() copy the skb to a linear one before calling into the security ops only when skb_cloned() is true. An skb that is not cloned but still carries externally-owned paged fragments (e.g. SKBFL_SHARED_FRAG set by splice() into a UDP socket via __ip_append_data, or a chained skb_has_frag_list()) falls through to the in-place decryption path, which binds the frag pages directly into the AEAD/skcipher SGL via skb_to_sgvec(). Extend the gate to also unshare when skb_has_frag_list() or skb_has_shared_frag() is true. This catches the splice-loopback vector and other externally-shared frag sources while preserving the zero-copy fast path for skbs whose frags are kernel-private (e.g. NIC page_pool RX, GRO). The OOM/trace handling already in place is reused.

Reference

• CVE-2026-43284
• CVE-2026-43500

Revision