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CVE-2024-35839

Disclosure Date: May 17, 2024 •
CVE-2024-35839
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Description

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

netfilter: bridge: replace physindev with physinif in nf_bridge_info

An skb can be added to a neigh->arp_queue while waiting for an arp
reply. Where original skb’s skb->dev can be different to neigh’s
neigh->dev. For instance in case of bridging dnated skb from one veth to
another, the skb would be added to a neigh->arp_queue of the bridge.

As skb->dev can be reset back to nf_bridge->physindev and used, and as
there is no explicit mechanism that prevents this physindev from been
freed under us (for instance neigh_flush_dev doesn’t cleanup skbs from
different device’s neigh queue) we can crash on e.g. this stack:

arp_process
neigh_update

skb = __skb_dequeue(&neigh->arp_queue)
  neigh_resolve_output(..., skb)
    ...
      br_nf_dev_xmit
        br_nf_pre_routing_finish_bridge_slow
          skb->dev = nf_bridge->physindev
          br_handle_frame_finish

Let’s use plain ifindex instead of net_device link. To peek into the
original net_device we will use dev_get_by_index_rcu(). Thus either we
get device and are safe to use it or we don’t get it and drop skb.

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CVSS V3 Severity and Metrics
Base Score:
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Impact Score:
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Exploitability Score:
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Vector:
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Attack Vector (AV):
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Attack Complexity (AC):
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Privileges Required (PR):
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User Interaction (UI):
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Scope (S):
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Integrity (I):
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Availability (A):
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General Information

Offensive Application
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Utility Class
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Ports
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OS
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Vulnerable Versions
Linux 7ae19ee81ca5
Linux not down converted
Prerequisites
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Discovered By
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PoC Author
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Metasploit Module
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Reporter
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Vendors

  • Linux

Products

  • Linux
Technical Analysis