Summary
In the Linux kernel, the following vulnerability has been resolved: net_sched: hfsc: Address...
In the Linux kernel, the following vulnerability has been resolved:
net_sched: hfsc: Address reentrant enqueue adding class to eltree twice
Savino says:
"We are writing to report that this recent patch
(141d34391abbb315d68556b7c67ad97885407547) [1]
can be bypassed, and a UAF can still occur when HFSC is utilized with
NETEM.
The patch only checks the cl->cl_nactive field to determine whether
it is the first insertion or not [2], but this field is only
incremented by init_vf [3].
By using HFSC_RSC (which uses init_ed) [4], it is possible to bypass the
check and insert the class twice in the eltree.
Under normal conditions, this would lead to an infinite loop in
hfsc_dequeue for the reasons we already explained in this report [5].
However, if TBF is added as root qdisc and it is configured with a
very low rate,
it can be utilized to prevent packets from being dequeued.
This behavior can be exploited to perform subsequent insertions in the
HFSC eltree and cause a UAF."
To fix both the UAF and the infinite loop, with netem as an hfsc child,
check explicitly in hfsc_enqueue whether the class is already in the eltree
whenever the HFSC_RSC flag is set.
[1] https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=141d34391abbb315d68556b7c67ad97885407547
[2] https://elixir.bootlin.com/linux/v6.15-rc5/source/net/sched/sch_hfsc.c#L1572
[3] https://elixir.bootlin.com/linux/v6.15-rc5/source/net/sched/sch_hfsc.c#L677
[4] https://elixir.bootlin.com/linux/v6.15-rc5/source/net/sched/sch_hfsc.c#L1574
[5] https://lore.kernel.org/netdev/8DuRWwfqjoRDLDmBMlIfbrsZg9Gx50DHJc1ilxsEBNe2D6NMoigR_eIRIG0LOjMc3r10nUUZtArXx4oZBIdUfZQrwjcQhdinnMis_0G7VEk=@willsroot.io/T/#u
Impact
CVE-2025-38001 has a CVSS score of 5.5 (Medium). The vector is requires local access, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. No fixed version is listed yet, so configuration controls and monitoring matter more in the interim.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2025-38001? CVE-2025-38001 is a medium-severity security vulnerability. No fixed version is listed yet.
- How severe is CVE-2025-38001? CVE-2025-38001 has a CVSS score of 5.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Is there a fix for CVE-2025-38001? No fixed version is listed for CVE-2025-38001 yet. Monitor the advisory for updates and apply mitigations in the interim.
- Is CVE-2025-38001 exploitable, and should I be worried? Whether CVE-2025-38001 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2025-38001 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.