CVE-2025-37890 | net_sched: hfsc: Fix a UAF vulnerability in class with netem as child qdisc

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/

Published: 2025-05-16 Last update: 2025-11-17 Assigner: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2025-37890 is rated Low Risk (39.6/100): CVSS High severity, with low exploitation likelihood (EPSS 0.08%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2025-37890

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-03-12 0.02% 0.08% +0.07%
2 2025-11-18 0.06% 0.02% -0.04%
3 2025-10-24 — 0.06% —

Full EPSS history (6 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2025-37890

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.8 3.1 HIGH
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 1.8 5.9 [email protected]

Weakness enumeration for CVE-2025-37890

OS Trackers for CVE-2025-37890

vendor priority summary link
debian not yet assigned CVE-2025-37890 not yet assigned priority: Debian including 2 source packages (linux, linux-6.1), 6 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 6. https://security-tracker.debian.org/tracker/CVE-2025-37890
redhat high — https://access.redhat.com/security/cve/CVE-2025-37890
suse high — https://www.suse.com/security/cve/CVE-2025-37890/
ubuntu medium CVE-2025-37890 medium priority: Ubuntu including 158 source packages (linux, linux-allwinner-5.19, …), 1551 status rows across 10 suites (bionic, focal, jammy, noble, oracular, plucky, questing, trusty, upstream, xenial): DNE 1145, released 204, ignored 147, not-affected 52, needs-triage 2, needed 1. https://ubuntu.com/security/CVE-2025-37890

Affected software / configurations for CVE-2025-37890

Vendor Product Version Raw CPE
linux linux_kernel >= 5.0.1, < 5.4.294 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 5.5, < 5.10.238 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 5.11, < 5.15.182 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 5.16, < 6.1.138 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 6.2, < 6.6.90 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 6.7, < 6.12.28 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 6.13, < 6.14.6 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel 5.0 cpe:2.3:o:linux:linux_kernel:5.0:-:*:*:*:*:*:*
linux linux_kernel 5.0 cpe:2.3:o:linux:linux_kernel:5.0:rc3:*:*:*:*:*:*
linux linux_kernel 5.0 cpe:2.3:o:linux:linux_kernel:5.0:rc4:*:*:*:*:*:*
linux linux_kernel 5.0 cpe:2.3:o:linux:linux_kernel:5.0:rc5:*:*:*:*:*:*
linux linux_kernel 5.0 cpe:2.3:o:linux:linux_kernel:5.0:rc6:*:*:*:*:*:*
linux linux_kernel 5.0 cpe:2.3:o:linux:linux_kernel:5.0:rc7:*:*:*:*:*:*
linux linux_kernel 5.0 cpe:2.3:o:linux:linux_kernel:5.0:rc8:*:*:*:*:*:*
linux linux_kernel 6.15 cpe:2.3:o:linux:linux_kernel:6.15:rc1:*:*:*:*:*:*
linux linux_kernel 6.15 cpe:2.3:o:linux:linux_kernel:6.15:rc2:*:*:*:*:*:*
linux linux_kernel 6.15 cpe:2.3:o:linux:linux_kernel:6.15:rc3:*:*:*:*:*:*
linux linux_kernel 6.15 cpe:2.3:o:linux:linux_kernel:6.15:rc4:*:*:*:*:*:*
debian debian_linux 11.0 cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*

References for CVE-2025-37890

URL Tags
https://git.kernel.org/stable/c/141d34391abbb315d68556b7c67ad97885407547 Patch
https://git.kernel.org/stable/c/273bbcfa53541cde38b2003ad88a59b770306421 Patch
https://git.kernel.org/stable/c/2e7093c7a8aba5d4f8809f271488e5babe75e202 Patch
https://git.kernel.org/stable/c/6082a87af4c52f58150d40dec1716011d871ac21 Patch
https://git.kernel.org/stable/c/8df7d37d626430035b413b97cee18396b3450bef Patch
https://git.kernel.org/stable/c/ac39fd4a757584d78ed062d4f6fd913f83bd98b5 Patch
https://git.kernel.org/stable/c/e0cf8ee23e1915431f262a7b2dee0c7a7d699af0 Patch
https://git.kernel.org/stable/c/e3e949a39a91d1f829a4890e7dfe9417ac72e4d0 Patch
https://lists.debian.org/debian-lts-announce/2025/08/msg00010.html Mailing List
https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html Mailing List
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