CVE-2025-39848

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

ax25: properly unshare skbs in ax25_kiss_rcv()

Bernard Pidoux reported a regression apparently caused by commit c353e8983e0d ("net: introduce per netns packet chains").

skb->dev becomes NULL and we crash in __netif_receive_skb_core().

Before above commit, different kind of bugs or corruptions could happen without a major crash.

But the root cause is that ax25_kiss_rcv() can queue/mangle input skb without checking if this skb is shared or not.

Many thanks to Bernard Pidoux for his help, diagnosis and tests.

We had a similar issue years ago fixed with commit 7aaed57c5c28 ("phonet: properly unshare skbs in phonet_rcv()").

Red Hat Enterprise Linux is not affected by this vulnerability because support for the AX.25 network protocol is not enabled in supported Red Hat kernels. The flaw occurs when shared network buffers are handled improperly during packet reception, potentially causing a kernel panic and denial of service. Because the vulnerable subsystem is omitted from enterprise kernel builds, default installations are not exposed to this flaw.