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CVE-2026-43254

Estado: AnalizadaAlta (7.5)—

In the Linux kernel, the following vulnerability has been resolved:

ovpn: tcp - fix packet extraction from stream

When processing TCP stream data in ovpn_tcp_recv, we receive large cloned skbs from __strp_rcv that may contain multiple coalesced packets. The current implementation has two bugs:

Fix both issues by allocating a new skb for each openvpn packet and using skb_copy_bits to extract only the packet content into the new buffer, skipping the 2-byte length prefix. Also, check the length before invoking the function that performs the allocation to avoid creating an invalid skb.

If the packet has to be forwarded to userspace the 2-byte prefix can be pushed to the head safely, without misalignment.

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As a side effect, this approach also avoids the expensive linearization that pskb_pull triggers on cloned skbs with page fragments. In testing, this resulted in TCP throughput improvements of up to 74%.

Detalles técnicos trazas, registros y código del informe original
1. Header offset overflow: Using pskb_pull with large offsets on
   coalesced skbs causes skb->data - skb->head to exceed the u16 storage
   of skb->network_header. This causes skb_reset_network_header to fail
   on the inner decapsulated packet, resulting in packet drops.

2. Unaligned protocol headers: Extracting packets from arbitrary
   positions within the coalesced TCP stream provides no alignment
   guarantees for the packet data causing performance penalties on
   architectures without efficient unaligned access. Additionally,
   openvpn's 2-byte length prefix on TCP packets causes the subsequent
   4-byte opcode and packet ID fields to be inherently misaligned.

CVSS

Probabilidad de explotación (EPSS)

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

🎯 Técnicas ATT&CK

Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.

CVE-2026-43254 describe un desbordamiento en el kernel de Linux (CWE-190) accesible desde red sin privilegios (AV:N/PR:N) que causa negación de servicio (A:H). El vector sugiere T1190 (explotación remota), aunque la vulnerabilidad radica en manejo de datos en stream TCP; los impactos son DoS de CPU/

Inferido por nuestro agente de análisis a partir de la descripción oficial, el vector CVSS y la CWE, y comprobado por un supervisor. Puede contener errores.

🛡️ Mitigaciones ATT&CK que cubren estas técnicas

Filter Network TrafficApplication Isolation and SandboxingExploit ProtectionUpdate SoftwareVulnerability ScanningThreat Intelligence Program

Tecnologías afectadas (1)

Linux — Linux Kernel

CWE

Referencias

JSON original (NVD)

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{
  "id": "CVE-2026-43254",
  "cveTags": [],
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        }
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  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\novpn: tcp - fix packet extraction from stream\n\nWhen processing TCP stream data in ovpn_tcp_recv, we receive large\ncloned skbs from __strp_rcv that may contain multiple coalesced packets.\nThe current implementation has two bugs:\n\n1. Header offset overflow: Using pskb_pull with large offsets on\n   coalesced skbs causes skb->data - skb->head to exceed the u16 storage\n   of skb->network_header. This causes skb_reset_network_header to fail\n   on the inner decapsulated packet, resulting in packet drops.\n\n2. Unaligned protocol headers: Extracting packets from arbitrary\n   positions within the coalesced TCP stream provides no alignment\n   guarantees for the packet data causing performance penalties on\n   architectures without efficient unaligned access. Additionally,\n   openvpn's 2-byte length prefix on TCP packets causes the subsequent\n   4-byte opcode and packet ID fields to be inherently misaligned.\n\nFix both issues by allocating a new skb for each openvpn packet and\nusing skb_copy_bits to extract only the packet content into the new\nbuffer, skipping the 2-byte length prefix. Also, check the length before\ninvoking the function that performs the allocation to avoid creating an\ninvalid skb.\n\nIf the packet has to be forwarded to userspace the 2-byte prefix can be\npushed to the head safely, without misalignment.\n\nAs a side effect, this approach also avoids the expensive linearization\nthat pskb_pull triggers on cloned skbs with page fragments. In testing,\nthis resulted in TCP throughput improvements of up to 74%."
    }
  ],
  "lastModified": "2026-06-17T10:49:15.090",
  "configurations": [
    {
      "nodes": [
        {
          "negate": false,
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}