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Date: Tue, 7 Sep 2021 14:09:52 +0530
From: Rohit Keshri <>
Subject: CVE-2021-3715 Linux kernel: use-after-free in
 route4_change() in net/sched/cls_route.c

Hello Team,

A flaw was found in the "Routing decision" classifier in the Linux kernel's
Traffic Control networking subsystem in the way it handled changing of
classification filters, leading to a use-after-free condition. This flaw
allows unprivileged local users to escalate their privileges on the system.
The highest threat from this vulnerability is confidentiality, integrity,
as well as system availability.

This issue was fixed in the upstream Kernel 5.10 onward with ef299cc3fa1a9

This problem is considered a security threat because unprivileged
user/network namespaces can escalate privileges on the system.

'CVE-2021-3715' was assigned by Red Hat.

* acks (Zhenpeng Lin)

* Description from the reporter:

"Originally the bug was found by Syzkaller in
It shows a warning bug effect that is not exploitable, seemingly.
However, the bug can be turned into a use-after-free bug and eventually
results in a working exploit, with all the mitigation in centos being
bypassed." from zhenpeng

Updated packages for Red Hat are currently in QE and will be released when

Rohit Keshri / Red Hat Product Security Team
PGP: OX01BC 858A 07B7 15C8 EF33 BFE2 2EEB 0CBC 84A4 4C2D for urgent response

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