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Linux KernelOperating system · Linux

CVE-2025-37890

HIGH · 7.8 CVSS v3.1 Published 2025-05-16
Fix available
A fix is available. Upgrade to 5.4.294 / 5.10.238 or later.
See remediation →
80/100
Remediation priority · High
Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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/

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis
How this class of weakness works · CWE-416

Memory is used after it has been freed, so its contents — now potentially attacker-controlled — drive the program's behaviour. With careful heap grooming this becomes code execution. The fix requires disciplined ownership of memory and often a targeted rework of the object lifecycle.

General guidance for the use after free class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Linux KernelOperating system
Affected:>= 5.0.1, < 5.4.294>= 5.5, < 5.10.238>= 5.11, < 5.15.182>= 5.16, < 6.1.138>= 6.2, < 6.6.90>= 6.7, < 6.12.28>= 6.13, < 6.14.6= 5.0= 6.15
Debian LinuxOperating system
Affected:= 11.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 5.4.294 / 5.10.238 / 5.15.182 or later
Fixed in 5.4.2945.10.2385.15.182
Vendor patch git.kernel.org →
Recommended fix High confidence

Linux kernel >= 6.1.138, or >= 5.15.182, or >= 5.10.238, or >= 5.4.294 (Debian 11: upgrade to a kernel version incorporating the fix from commit 141d34391abbb315d68556b7c67ad97885407547)

  1. 1. Identify the current kernel version using `uname -r` or `hostnamectl`
  2. 2. Check if the system uses HFSC qdisc with netem child by running `tc qdisc show` and inspecting qdisc configuration
  3. 3. For Debian 11 systems, apply kernel updates from Debian's security repository: `apt update && apt install linux-image-<version>`
  4. 4. Reboot into the updated kernel
  5. 5. After reboot, verify the kernel version is >= 6.1.138 (or >= 5.15.182, >= 5.10.238, or >= 5.4.294 depending on the branch you upgraded to)
  6. 6. Verify HFSC functionality with netem child qdisc works correctly: `tc qdisc show` and test network traffic
Caveat Kernel upgrades may require system reboot and could introduce compatibility issues with proprietary kernel modules or specific hardware drivers; test in staging environment first

Generated from the published advisory — verify against the referenced sources before acting.

We can perform the upgrade in your staging environment and verify nothing breaks — typical engagement from $3,200. Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2025-37890 in production — separate from our analysis above.

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