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CVE-2025-39673

Full vulnerability record from the local CVENow database.

Description

In the Linux kernel, the following vulnerability has been resolved: ppp: fix race conditions in ppp_fill_forward_path ppp_fill_forward_path() has two race conditions: 1. The ppp->channels list can change between list_empty() and list_first_entry(), as ppp_lock() is not held. If the only channel is deleted in ppp_disconnect_channel(), list_first_entry() may access an empty head or a freed entry, and trigger a panic. 2. pch->chan can be NULL. When ppp_unregister_channel() is called, pch->chan is set to NULL before pch is removed from ppp->channels. Fix these by using a lockless RCU approach: - Use list_first_or_null_rcu() to safely test and access the first list entry. - Convert list modifications on ppp->channels to their RCU variants and add synchronize_net() after removal. - Check for a NULL pch->chan before dereferencing it.

Severity
MEDIUM
CVSS score
4.7 (v3.1)
Vulnerability status
Modified
Source identifier
416baaa9-dc9f-4396-8d5f-8c081fb06d67
Published
2025-09-05 18:15:43.230000
Last modified
2026-10-19 21:10:00.160000
View original CVE JSON 
{
  "id": "CVE-2025-39673",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "published": "2025-09-05T18:15:43.230",
  "lastModified": "2026-10-19T21:10:00.160",
  "vulnStatus": "Modified",
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    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nppp: fix race conditions in ppp_fill_forward_path\n\nppp_fill_forward_path() has two race conditions:\n\n1. The ppp->channels list can change between list_empty() and\n   list_first_entry(), as ppp_lock() is not held. If the only channel\n   is deleted in ppp_disconnect_channel(), list_first_entry() may\n   access an empty head or a freed entry, and trigger a panic.\n\n2. pch->chan can be NULL. When ppp_unregister_channel() is called,\n   pch->chan is set to NULL before pch is removed from ppp->channels.\n\nFix these by using a lockless RCU approach:\n- Use list_first_or_null_rcu() to safely test and access the first list\n  entry.\n- Convert list modifications on ppp->channels to their RCU variants and\n  add synchronize_net() after removal.\n- Check for a NULL pch->chan before dereferencing it."
    },
    {
      "lang": "es",
      "value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\nppp: corregir condiciones de carrera en ppp_fill_forward_path\n\nppp_fill_forward_path() tiene dos condiciones de carrera:\n\n1. La lista ppp->channels puede cambiar entre list_empty() y list_first_entry(), ya que ppp_lock() no está retenido. Si el único canal es eliminado en ppp_disconnect_channel(), list_first_entry() puede acceder a una cabecera vacía o a una entrada liberada, y desencadenar un pánico.\n\n2. pch->chan puede ser NULL. Cuando se llama a ppp_unregister_channel(), pch->chan se establece en NULL antes de que pch sea eliminado de ppp->channels.\n\nCorregir esto utilizando un enfoque RCU sin bloqueo:\n- Usar list_first_or_null_rcu() para probar y acceder de forma segura a la primera entrada de la lista.\n- Convertir las modificaciones de la lista en ppp->channels a sus variantes RCU y añadir synchronize_net() después de la eliminación.\n- Comprobar si pch->chan es NULL antes de desreferenciarlo."
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