CVE-2026-99077 Ataque de canal lateral sobre el puerto efímero de sockets UDP en IPv4

Qué es CVE-2026-99077

Las excepciones FNHE por ICMP Fragmentation Needed y Redirect solo se creaban si el paquete UDP citado coincidía con un socket existente, lo que permite a atacantes fuera de ruta sondear la caché FNHE y descubrir el puerto efímero de un socket UDP conectado. Se crean las excepciones antes de la coincidencia con el socket.

Productos y versiones afectadas

• Linux

  • desde 4895c771c7f006b4b90f9d6b1d2210939ba57b38 hasta antes de be4fd05398f2b5e42029be70ee875fc749b8ce3a
  • desde 4895c771c7f006b4b90f9d6b1d2210939ba57b38 hasta antes de 4c3499f79f8c7e8561266bcc220a18538cec0458

• Linux

  • 3.6

Qué hacer

1. Verificá si usás Linux y en qué versión: el rango afectado figura arriba.
2. Actualizá a la versión corregida que indique el fabricante en su aviso (ver referencias) o aplicá la mitigación que publique.
3. Revisá registros y accesos de los sistemas expuestos para descartar que se haya aprovechado antes de corregir.

Calculadora CVSS

CVSS 3.1 · 7.4 ALTA

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

VECTOR DE ATAQUE (AV)

Red

COMPLEJIDAD DEL ATAQUE (AC)

Alta

PRIVILEGIOS REQUERIDOS (PR)

Ninguno

INTERACCIÓN DEL USUARIO (UI)

Ninguna

ALCANCE (S)

Sin cambio

CONFIDENCIALIDAD (C)

Alta

INTEGRIDAD (I)

Alta

DISPONIBILIDAD (A)

Ninguna

Abrir la calculadora completa →

Descripción original

In the Linux kernel, the following vulnerability has been resolved: ipv4: udp: Create exceptions before socket matching Currently, when ICMP Fragmentation Needed and Redirect Message packets are locally delivered and quote a UDP packet, a FIB nexthop exception (FNHE) is only created if the kernel can match the UDP packet to an existing socket. This behavior allows off-path attackers to conduct a side-channel attack on the FNHE cache in order to discover the ephemeral port used by a connected UDP socket. Commit 6457378fe796 ("ipv4: use siphash instead of Jenkins in fnhe_hashfun()") and commit 67d6d681e15b ("ipv4: make exception cache less predictible") tried to mitigate such attacks by making it harder for attackers to discover hash collisions in the FNHE cache and by randomizing the number of exceptions a hash bucket can hold, respectively. Unfortunately, both of the mitigations can be bypassed. Instead, mitigate such attacks by always creating a FNHE, even before trying to find a matching socket. Do that by calling ipv4_update_pmtu() and ipv4_redirect(), the helpers used when the quoted packet did not originate from a socket. This means that guesses (right or wrong) from an off-path attacker will always result in a FNHE being created or updated in the cache that the attacker can observe. Pass an oif of 0, in a similar fashion to icmp_err(). This is also the oif used by the socket path for sockets that are not bound to a device. Note that this does not allow attackers to create FNHEs that they could not create before, as both helpers can already be reached with little to no validation. For example, by sending an ICMP error that quotes an ICMP Echo Reply or one that quotes a UDP source port that matches a wildcard socket. Also note that in the good case (matched socket) the above scheme comes at the cost of an extra route lookup, as the no socket helpers perform their own lookup before the one performed by ipv4_sk_update_pmtu() / ipv4_sk_redirect(). When the two resolve to different nexthops, it also results in two exceptions being created for the same destination IP. One in the FNHE cache of the nexthop resolved by the no socket helpers and another in the FNHE cache of the nexthop used by the socket.

Referencias

• git.kernel.org/stable/c/be4fd05398f2b5e42029be70ee875fc749b8ce3a
• git.kernel.org/stable/c/4c3499f79f8c7e8561266bcc220a18538cec0458

Historial de la alerta

1. 23 OCT · 10:16VULNERABILIDAD Nueva vulnerabilidad detectada.

CÓMO SE HIZOResumen traducido automáticamente al español a partir de la descripción original. Ante dudas, la descripción original y las referencias del fabricante son la fuente de verdad. Cómo funciona.