CVE-2026-81003

Description

In the Linux kernel, the following vulnerability has been resolved: net/iucv: filter frames in afiucv_hs_rcv() by ingress device afiucv_hs_rcv() selects a socket from iucv_sk_list by matching four 8-byte name fields in the transport header alone. No check is made against the net_device the frame arrived on. This can cause a frame arriving on any netdev to be delivered to an AF_IUCV socket. Three problems follow. First, a frame arriving over HiperSockets can be delivered to a socket bound to the classic z/VM IUCV transport, which has iucv->hs_dev == NULL. iucv_sock_bind() takes the classic path whenever the requested userid matches iucv_userid, even on a guest that also has a HiperSockets device carrying the same identifier. The child socket created by afiucv_hs_callback_syn() for such a match inherits hs_dev = NULL and transport = AF_IUCV_TRANS_HIPER, so the first send() on it returns -ENODEV. The socket delivered to accept() is unusable. Second, a frame arriving on one netdev can be delivered to a socket bound to a different IQD device. Which can lead to - Accept-queue exhaustion (DoS) - Attacker-controlled peer identity in the child socket - Data injection into existing sockets - Fabric noise on the IQD fabric, where bogus replies are sent - killing established connections Third, all AF_IUCV sockets live in init_net, as iucv_sock_alloc() calls sk_alloc(&init_net, ...). But even frames arriving on netdev devices in a namespace can be delivered to an IUCV socket. So a process in an unprivileged user and network namespace holding only the CAP_NET_RAW capability valid within that namespace can send a raw ETH_P_AF_IUCV frame on its own lo device and have it matched against init_net sockets. Fix all three by skipping any socket whose hs_dev does not match the ingress device. A classic z/VM IUCV socket has hs_dev == NULL; the ingress dev is never NULL, so classic sockets are skipped automatically. An unbound HIPER socket also has hs_dev == NULL and is skipped. A bound HIPER socket is only reachable from the exact IQD device it was bound to. Because hs_dev is always a device in init_net (iucv_sock_bind() scans for_each_netdev_rcu(&init_net, ...) exclusively), a frame whose ingress device belongs to another namespace never matches any socket. Note that AF_IUCV over HiperSockets provides no per-connection authentication: no sequence numbers, no TLS, no nonce. The four name fields identifying a connection are exchanged in plaintext on the shared HiperSockets segment (VCHID). Any host on the same HiperSockets segment could spoof any frame type against an existing connection. That is a protocol-level property unchanged by this patch. The fix reduces the attack surface to peers present on the same HiperSockets segment.

Gravité et risque d'exploitation

CVE-2026-81003 obtient un score CVSS de 8.1/10, soit une gravité élevée. Selon le modèle EPSS, la probabilité qu'elle soit exploitée dans les 30 prochains jours est de 0.31 %, ce qui la place devant 22.2 % des CVE référencées.

Que faire ?

• Vérifiez si Linux (versions <=6.1.*, <3.2, <=6.12.*, 5.15.221, <dfac2936b83be00035ae176f8252e1c1e1de9207, 5.10.270, 0, <92e5c281f1caa287bb58292f2687c9e3ff3aa23e, 7.2.4, 6.1.188, <8e3763f1ccac3fc395f9af2b87114c023ced8a3f, 3881ac441f642d56503818123446f7298442236b, <=5.10.*, <=6.6.*, 6.6.157, <a7f0130a091724e69827ab58e74777a88747e892, <0a5af67e7184c6a0e155c317840bd64b37177af4, <=6.18.*, 3.2, <=7.2.*, <639828ad4d374056167391dbaffd13dd5e5e5ddb, <712330f8a4293cfd97b0d62b7c7dc01862a16b98, <=*, <=5.15.*, 6.18.50, <80230a18c164a4b5bbc048fe2768b219ac17bc5a, 6.12.109, 7.3) est présent sur votre parc.
• Appliquez le correctif ou la version corrigée indiqués dans les références de l'éditeur.
• À défaut de correctif, limitez l'exposition (filtrage réseau, désactivation du composant).
• Automatisez la détection : les agents CVE Heimdall (gratuits, open source) corrèlent l'inventaire de vos serveurs avec la base CVE.

Références

• https://git.kernel.org/stable/c/639828ad4d374056167391dbaffd13dd5e5e5ddb
• https://git.kernel.org/stable/c/92e5c281f1caa287bb58292f2687c9e3ff3aa23e
• https://git.kernel.org/stable/c/712330f8a4293cfd97b0d62b7c7dc01862a16b98
• https://git.kernel.org/stable/c/0a5af67e7184c6a0e155c317840bd64b37177af4
• https://git.kernel.org/stable/c/dfac2936b83be00035ae176f8252e1c1e1de9207
• https://git.kernel.org/stable/c/8e3763f1ccac3fc395f9af2b87114c023ced8a3f
• https://git.kernel.org/stable/c/a7f0130a091724e69827ab58e74777a88747e892
• https://git.kernel.org/stable/c/80230a18c164a4b5bbc048fe2768b219ac17bc5a