CVE-2025-38001: Linux kernel · net_sched: hfsc: Address reentrant enqueue adding class to eltree twice
Affects Linux kernelSource GCVE Database
Not known to be exploited · CVSS 7.8 High · fixed in 5.4.0-1148.158~18.04.1 : patch Linux kernel soon.
Data as of 26 Oct 2026, 13:47 UTC
- EPSS
- 0.5% chance of exploitation in 30 days – higher than 43% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- Patch
- Available – fixed in 5.4.0-1148.158~18.04.1, 5.4.0-1153.160~18.04.1, 5.4.0-1151.160~18.04.1 +89
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:HExploitation evidence
Disclosed: evidence found.
CVE published 6 Jun 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.
What to do
Upgrade to a fixed release listed under Affected software.
Patches and advisories
- ubuntu.com/security/notices/USN-7608-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7608-2 (opens in a new tab)
- ubuntu.com/security/notices/USN-7608-3 (opens in a new tab)
- ubuntu.com/security/notices/USN-7609-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7609-2 (opens in a new tab)
- ubuntu.com/security/notices/USN-7610-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7611-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7608-4 (opens in a new tab)
- ubuntu.com/security/notices/USN-7609-3 (opens in a new tab)
- ubuntu.com/security/notices/USN-7618-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7608-5 (opens in a new tab)
- ubuntu.com/security/notices/USN-7609-4 (opens in a new tab)
Affected software
| Product | Affected | Fixed in |
|---|---|---|
Ubuntu 25.10linux-azure-fdepkg:deb/ubuntu/linux-azure-fde?arch=source&distro=questingOther threats | Affected
| Fixed in– |
Ubuntu 24.04 LTSlinuxpkg:deb/ubuntu/linux?arch=source&distro=nobleOther threats | Affected
| Fixed in
|
Ubuntu 24.04 LTSlinux-awspkg:deb/ubuntu/linux-aws?arch=source&distro=nobleOther threats | Affected
| Fixed in
|
Ubuntu 24.04 LTSlinux-aws-6.14pkg:deb/ubuntu/linux-aws-6.14?arch=source&distro=nobleOther threats | Affected
| Fixed in
|
Ubuntu 24.04 LTSlinux-azurepkg:deb/ubuntu/linux-azure?arch=source&distro=nobleOther threats | Affected
| Fixed in
|
Ubuntu 24.04 LTSlinux-azure-6.11pkg:deb/ubuntu/linux-azure-6.11?arch=source&distro=nobleOther threats | Affected
| Fixed in
|
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
Description
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
References
- ubuntu.com/security/CVE-2025-38001 (opens in a new tab)
- cve.org/CVERecord?id=CVE-2025-38001 (opens in a new tab)
- git.kernel.org/stable/c/295f7c579b07b5b7cf2dffe485f71cc2f27647cb (opens in a new tab)
- git.kernel.org/stable/c/2c928b3a0b04a431ffcd6c8b7d88a267124a3a28 (opens in a new tab)
- git.kernel.org/stable/c/2f2190ce4ca972051cac6a8d7937448f8cb9673c (opens in a new tab)
- git.kernel.org/stable/c/39ed887b1dd2d6b720f87e86692ac3006cc111c8 (opens in a new tab)
- git.kernel.org/stable/c/4e38eaaabfb7fffbb371a51150203e19eee5d70e (opens in a new tab)
- git.kernel.org/stable/c/6672e6c00810056acaac019fe26cdc26fee8a66c (opens in a new tab)
- git.kernel.org/stable/c/a0ec22fa20b252edbe070a9de8501eef63c17ef5 (opens in a new tab)
- git.kernel.org/stable/c/e5bee633cc276410337d54b99f77fbc1ad8801e5 (opens in a new tab)
- ubuntu.com/security/notices/USN-7608-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7608-2 (opens in a new tab)
- ubuntu.com/security/notices/USN-7608-3 (opens in a new tab)
- ubuntu.com/security/notices/USN-7609-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7609-2 (opens in a new tab)
- ubuntu.com/security/notices/USN-7610-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7611-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7608-4 (opens in a new tab)
- ubuntu.com/security/notices/USN-7609-3 (opens in a new tab)
- ubuntu.com/security/notices/USN-7618-1 (opens in a new tab)