Monitor vulnerabilities like this one.
Sign up free to get alerted when software you use is affected.
7.8
CVE-2025-37797: Linux Kernel: HFSC Scheduler Can Crash System
CVE-2025-37797
Summary
A bug in the Linux kernel's traffic controller can cause the system to crash if a specific type of network traffic is handled. This can happen when certain network traffic is being analyzed and modified. To fix this, an additional check has been added to ensure the traffic queue is not empty before making certain changes.
What to do
No fix is available yet. Check with your software vendor for updates.
Affected software
| Vendor | Product | Affected versions |
|---|---|---|
| linux | linux_kernel |
>= 4.14.1, < 5.4.293 >= 5.5, < 5.10.237 >= 5.11, < 5.15.181 >= 5.16, < 6.1.136 >= 6.2, < 6.6.89 >= 6.7, < 6.12.26 >= 6.13, < 6.14.5 4.14 6.15 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* |
| debian | debian_linux |
11.0 cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:* |
Original title
In the Linux kernel, the following vulnerability has been resolved:
net_sched: hfsc: Fix a UAF vulnerability in class handling
This patch fixes a Use-After-Free vulnerability in the HFSC qdisc cl...
Original description
In the Linux kernel, the following vulnerability has been resolved:
net_sched: hfsc: Fix a UAF vulnerability in class handling
This patch fixes a Use-After-Free vulnerability in the HFSC qdisc class
handling. The issue occurs due to a time-of-check/time-of-use condition
in hfsc_change_class() when working with certain child qdiscs like netem
or codel.
The vulnerability works as follows:
1. hfsc_change_class() checks if a class has packets (q.qlen != 0)
2. It then calls qdisc_peek_len(), which for certain qdiscs (e.g.,
codel, netem) might drop packets and empty the queue
3. The code continues assuming the queue is still non-empty, adding
the class to vttree
4. This breaks HFSC scheduler assumptions that only non-empty classes
are in vttree
5. Later, when the class is destroyed, this can lead to a Use-After-Free
The fix adds a second queue length check after qdisc_peek_len() to verify
the queue wasn't emptied.
net_sched: hfsc: Fix a UAF vulnerability in class handling
This patch fixes a Use-After-Free vulnerability in the HFSC qdisc class
handling. The issue occurs due to a time-of-check/time-of-use condition
in hfsc_change_class() when working with certain child qdiscs like netem
or codel.
The vulnerability works as follows:
1. hfsc_change_class() checks if a class has packets (q.qlen != 0)
2. It then calls qdisc_peek_len(), which for certain qdiscs (e.g.,
codel, netem) might drop packets and empty the queue
3. The code continues assuming the queue is still non-empty, adding
the class to vttree
4. This breaks HFSC scheduler assumptions that only non-empty classes
are in vttree
5. Later, when the class is destroyed, this can lead to a Use-After-Free
The fix adds a second queue length check after qdisc_peek_len() to verify
the queue wasn't emptied.
nvd CVSS3.1
7.8
Vulnerability type
CWE-416
Use After Free
- https://git.kernel.org/stable/c/20d584a33e480ae80d105f43e0e7b56784da41b9 Patch
- https://git.kernel.org/stable/c/28b09a067831f7317c3841812276022d6c940677 Patch
- https://git.kernel.org/stable/c/39b9095dd3b55d9b2743df038c32138efa34a9de Patch
- https://git.kernel.org/stable/c/3aa852e3605000d5c47035c3fc3a986d14ccfa9f Patch
- https://git.kernel.org/stable/c/3df275ef0a6ae181e8428a6589ef5d5231e58b5c Patch
- https://git.kernel.org/stable/c/86cd4641c713455a4f1c8e54c370c598c2b1cee0 Patch
- https://git.kernel.org/stable/c/bb583c88d23b72d8d16453d24856c99bd93dadf5 Patch
- https://git.kernel.org/stable/c/fcc8ede663569c704fb00a702973bd6c00373283 Patch
- https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html Mailing List Third Party Advisory
- https://lists.debian.org/debian-lts-announce/2025/05/msg00045.html Mailing List Third Party Advisory
Published: 2 May 2025 · Updated: 2 Jul 2026 · First seen: 7 Mar 2026