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CVE-2025-37890 – Linux Kernel net_sched hfsc UAF Vulnerability

The following table lists the changes that have been made to the
CVE-2025-37890 vulnerability over time.

Vulnerability history details can be useful for understanding the evolution
of a vulnerability, and for identifying the most recent changes that may
impact the vulnerability’s severity, exploitability, or other characteristics.

  • New CVE Received
    by 416baaa9-dc9f-4396-8d5f-8c081fb06d67

    May. 16, 2025

    Action Type Old Value New Value
    Added Description In the Linux kernel, the following vulnerability has been resolved:

    net_sched: hfsc: Fix a UAF vulnerability in class with netem as child qdisc

    As described in Gerrard’s report [1], we have a UAF case when an hfsc class
    has a netem child qdisc. The crux of the issue is that hfsc is assuming
    that checking for cl->qdisc->q.qlen == 0 guarantees that it hasn’t inserted
    the class in the vttree or eltree (which is not true for the netem
    duplicate case).

    This patch checks the n_active class variable to make sure that the code
    won’t insert the class in the vttree or eltree twice, catering for the
    reentrant case.

    [1] https://lore.kernel.org/netdev/CAHcdcOm+03OD2j6R0=YHKqmy=VgJ8xEOKuP6c7mSgnp-TEJJbw@mail.gmail.com/
    Added Reference https://git.kernel.org/stable/c/141d34391abbb315d68556b7c67ad97885407547
    Added Reference https://git.kernel.org/stable/c/2e7093c7a8aba5d4f8809f271488e5babe75e202
    Added Reference https://git.kernel.org/stable/c/6082a87af4c52f58150d40dec1716011d871ac21
    Added Reference https://git.kernel.org/stable/c/8df7d37d626430035b413b97cee18396b3450bef
    Added Reference https://git.kernel.org/stable/c/ac39fd4a757584d78ed062d4f6fd913f83bd98b5
    Added Reference https://git.kernel.org/stable/c/e3e949a39a91d1f829a4890e7dfe9417ac72e4d0
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