CVE-2025-37797
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.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.21%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
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.
- CVSS 3.1
- 7.8 HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- EPSS
- 0.21% probability · 12th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-416
- Affected
- linux/linux kernel · debian/debian linux
- Source
- 416baaa9-dc9f-4396-8d5f-8c081fb06d67
References
- https://git.kernel.org/stable/c/20d584a33e480ae80d105f43e0e7b56784da41b9Patch
- https://git.kernel.org/stable/c/28b09a067831f7317c3841812276022d6c940677Patch
- https://git.kernel.org/stable/c/39b9095dd3b55d9b2743df038c32138efa34a9dePatch
- https://git.kernel.org/stable/c/3aa852e3605000d5c47035c3fc3a986d14ccfa9fPatch
- https://git.kernel.org/stable/c/3df275ef0a6ae181e8428a6589ef5d5231e58b5cPatch
- https://git.kernel.org/stable/c/86cd4641c713455a4f1c8e54c370c598c2b1cee0Patch
- https://git.kernel.org/stable/c/bb583c88d23b72d8d16453d24856c99bd93dadf5Patch
- https://git.kernel.org/stable/c/fcc8ede663569c704fb00a702973bd6c00373283Patch
- https://lists.debian.org/debian-lts-announce/2025/05/msg00030.htmlMailing List, Third Party Advisory
- https://lists.debian.org/debian-lts-announce/2025/05/msg00045.htmlMailing List, Third Party Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.