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/
Advisories
Source ID Title
Debian DLA Debian DLA DLA-4271-1 linux-6.1 security update
Debian DLA Debian DLA DLA-4327-1 linux security update
Debian DSA Debian DSA DSA-5925-1 linux security update
EUVD EUVD EUVD-2025-15440 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/
Ubuntu USN Ubuntu USN USN-7608-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-7608-2 Linux kernel (FIPS) vulnerabilities
Ubuntu USN Ubuntu USN USN-7608-3 Linux kernel (Real-time) vulnerabilities
Ubuntu USN Ubuntu USN USN-7608-4 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-7608-5 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-7608-6 Linux kernel (Xilinx ZynqMP) vulnerabilities
Ubuntu USN Ubuntu USN USN-7608-7 Linux kernel (Azure) vulnerabilities
Ubuntu USN Ubuntu USN USN-7609-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-7609-2 Linux kernel (Real-time) vulnerabilities
Ubuntu USN Ubuntu USN USN-7609-3 Linux kernel (IBM) vulnerabilities
Ubuntu USN Ubuntu USN USN-7609-4 Linux kernel (Azure) vulnerabilities
Ubuntu USN Ubuntu USN USN-7609-5 Linux kernel (Azure) vulnerabilities
Ubuntu USN Ubuntu USN USN-7610-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-7610-2 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-7610-3 Linux kernel (Low Latency) vulnerabilities
Ubuntu USN Ubuntu USN USN-7611-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-7611-2 Linux kernel (Azure) vulnerabilities
Ubuntu USN Ubuntu USN USN-7611-3 Linux kernel (AWS) vulnerabilities
Ubuntu USN Ubuntu USN USN-7611-4 Linux kernel (Oracle) vulnerabilities
Ubuntu USN Ubuntu USN USN-7618-1 Linux kernel (OEM) vulnerabilities
Ubuntu USN Ubuntu USN USN-7628-1 Linux kernel (Azure) vulnerabilities
Ubuntu USN Ubuntu USN USN-7653-1 Linux kernel (HWE) vulnerabilities
Ubuntu USN Ubuntu USN USN-7655-1 Linux kernel (Intel IoTG) vulnerabilities
Ubuntu USN Ubuntu USN USN-7665-2 Linux kernel (AWS) vulnerabilities
Ubuntu USN Ubuntu USN USN-7671-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-7671-2 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-7671-3 Linux kernel (IoT) vulnerabilities
Ubuntu USN Ubuntu USN USN-7686-1 Linux kernel (Raspberry Pi) vulnerabilities
Ubuntu USN Ubuntu USN USN-7712-1 Linux kernel (Azure FIPS) vulnerabilities
Ubuntu USN Ubuntu USN USN-7712-2 Linux kernel (Azure) vulnerabilities
Fixes

Solution

No solution given by the vendor.


Workaround

No workaround given by the vendor.

History

Mon, 17 Nov 2025 17:15:00 +0000

Type Values Removed Values Added
First Time appeared Debian
Debian debian Linux
Weaknesses CWE-416
CPEs cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*
cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
cpe:2.3:o:linux:linux_kernel:5.0:-:*:*:*:*:*:*
cpe:2.3:o:linux:linux_kernel:5.0:rc3:*:*:*:*:*:*
cpe:2.3:o:linux:linux_kernel:5.0:rc4:*:*:*:*:*:*
cpe:2.3:o:linux:linux_kernel:5.0:rc5:*:*:*:*:*:*
cpe:2.3:o:linux:linux_kernel:5.0:rc6:*:*:*:*:*:*
cpe:2.3:o:linux:linux_kernel:5.0:rc7:*:*:*:*:*:*
cpe:2.3:o:linux:linux_kernel:5.0:rc8:*:*:*:*:*:*
cpe:2.3:o:linux:linux_kernel:6.15:rc1:*:*:*:*:*:*
cpe:2.3:o:linux:linux_kernel:6.15:rc2:*:*:*:*:*:*
cpe:2.3:o:linux:linux_kernel:6.15:rc3:*:*:*:*:*:*
cpe:2.3:o:linux:linux_kernel:6.15:rc4:*:*:*:*:*:*
Vendors & Products Debian
Debian debian Linux
Metrics cvssV3_1

{'score': 4.7, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H'}

cvssV3_1

{'score': 7.8, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'}


Mon, 03 Nov 2025 20:30:00 +0000

Type Values Removed Values Added
References

Mon, 03 Nov 2025 18:30:00 +0000

Type Values Removed Values Added
References

Wed, 18 Jun 2025 16:00:00 +0000

Type Values Removed Values Added
Metrics cvssV3_1

{'score': 7.0, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H'}

threat_severity

Important

cvssV3_1

{'score': 4.7, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H'}

threat_severity

Moderate


Thu, 12 Jun 2025 19:00:00 +0000

Type Values Removed Values Added
Metrics cvssV3_1

{'score': 5.5, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'}

threat_severity

Moderate

cvssV3_1

{'score': 7.0, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H'}

threat_severity

Important


Wed, 04 Jun 2025 13:00:00 +0000


Tue, 20 May 2025 02:30:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

cvssV3_1

{'score': 5.5, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'}

threat_severity

Moderate


Fri, 16 May 2025 13:15:00 +0000

Type Values Removed Values 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/
Title net_sched: hfsc: Fix a UAF vulnerability in class with netem as child qdisc
References

cve-icon MITRE

Status: PUBLISHED

Assigner: Linux

Published:

Updated: 2025-11-03T19:57:02.260Z

Reserved: 2025-04-16T04:51:23.963Z

Link: CVE-2025-37890

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Analyzed

Published: 2025-05-16T13:15:52.437

Modified: 2025-11-17T17:11:57.840

Link: CVE-2025-37890

cve-icon Redhat

Severity : Moderate

Publid Date: 2025-05-16T00:00:00Z

Links: CVE-2025-37890 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2025-06-23T19:32:00Z