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CVE-2025-39766
net/sched: Make cake_enqueue return NET_XMIT_CN when past buffer_limit
Description

In the Linux kernel, the following vulnerability has been resolved: net/sched: Make cake_enqueue return NET_XMIT_CN when past buffer_limit The following setup can trigger a WARNING in htb_activate due to the condition: !cl->leaf.q->q.qlen tc qdisc del dev lo root tc qdisc add dev lo root handle 1: htb default 1 tc class add dev lo parent 1: classid 1:1 \ htb rate 64bit tc qdisc add dev lo parent 1:1 handle f: \ cake memlimit 1b ping -I lo -f -c1 -s64 -W0.001 127.0.0.1 This is because the low memlimit leads to a low buffer_limit, which causes packet dropping. However, cake_enqueue still returns NET_XMIT_SUCCESS, causing htb_enqueue to call htb_activate with an empty child qdisc. We should return NET_XMIT_CN when packets are dropped from the same tin and flow. I do not believe return value of NET_XMIT_CN is necessary for packet drops in the case of ack filtering, as that is meant to optimize performance, not to signal congestion.

INFO

Published Date :

Sept. 11, 2025, 5:15 p.m.

Last Modified :

Sept. 11, 2025, 5:15 p.m.

Remotely Exploit :

No

Source :

416baaa9-dc9f-4396-8d5f-8c081fb06d67
Affected Products

The following products are affected by CVE-2025-39766 vulnerability. Even if cvefeed.io is aware of the exact versions of the products that are affected, the information is not represented in the table below.

ID Vendor Product Action
1 Linux linux_kernel
: Total Affected Vendor : 1 | Products : 1
Solution
Apply kernel updates to fix packet dropping issues and prevent system instability.
  • Update the Linux kernel to the latest stable version.
  • Review and apply any specific patches related to net/sched module.
  • Verify the integrity of the network scheduler configuration.
  • Test system stability after applying updates.
References to Advisories, Solutions, and Tools

Here, you will find a curated list of external links that provide in-depth information, practical solutions, and valuable tools related to CVE-2025-39766.

URL Resource
https://git.kernel.org/stable/c/0dacfc5372e314d1219f03e64dde3ab495a5a25e
https://git.kernel.org/stable/c/15de71d06a400f7fdc15bf377a2552b0ec437cf5
https://git.kernel.org/stable/c/62d591dde4defb1333d202410609c4ddeae060b3
https://git.kernel.org/stable/c/710866fc0a64eafcb8bacd91bcb1329eb7e5035f
https://git.kernel.org/stable/c/7689ab22de36f8db19095f6bdf11f28cfde92f5c
https://git.kernel.org/stable/c/aa12ee1c1bd260943fd6ab556d8635811c332eeb
https://git.kernel.org/stable/c/de04ddd2980b48caa8d7e24a7db2742917a8b280
https://git.kernel.org/stable/c/ff57186b2cc39766672c4c0332323933e5faaa88
CWE - Common Weakness Enumeration

While CVE identifies specific instances of vulnerabilities, CWE categorizes the common flaws or weaknesses that can lead to vulnerabilities. CVE-2025-39766 is associated with the following CWEs:

Common Attack Pattern Enumeration and Classification (CAPEC)

Common Attack Pattern Enumeration and Classification (CAPEC) stores attack patterns, which are descriptions of the common attributes and approaches employed by adversaries to exploit the CVE-2025-39766 weaknesses.

We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).

Results are limited to the first 15 repositories due to potential performance issues.

The following list is the news that have been mention CVE-2025-39766 vulnerability anywhere in the article.

Results are limited to the first 20 news articles due to potential performance issues.

The following table lists the changes that have been made to the CVE-2025-39766 vulnerability over time.

Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.

  • New CVE Received by 416baaa9-dc9f-4396-8d5f-8c081fb06d67

    Sep. 11, 2025

    Action Type Old Value New Value
    Added Description In the Linux kernel, the following vulnerability has been resolved: net/sched: Make cake_enqueue return NET_XMIT_CN when past buffer_limit The following setup can trigger a WARNING in htb_activate due to the condition: !cl->leaf.q->q.qlen tc qdisc del dev lo root tc qdisc add dev lo root handle 1: htb default 1 tc class add dev lo parent 1: classid 1:1 \ htb rate 64bit tc qdisc add dev lo parent 1:1 handle f: \ cake memlimit 1b ping -I lo -f -c1 -s64 -W0.001 127.0.0.1 This is because the low memlimit leads to a low buffer_limit, which causes packet dropping. However, cake_enqueue still returns NET_XMIT_SUCCESS, causing htb_enqueue to call htb_activate with an empty child qdisc. We should return NET_XMIT_CN when packets are dropped from the same tin and flow. I do not believe return value of NET_XMIT_CN is necessary for packet drops in the case of ack filtering, as that is meant to optimize performance, not to signal congestion.
    Added Reference https://git.kernel.org/stable/c/0dacfc5372e314d1219f03e64dde3ab495a5a25e
    Added Reference https://git.kernel.org/stable/c/15de71d06a400f7fdc15bf377a2552b0ec437cf5
    Added Reference https://git.kernel.org/stable/c/62d591dde4defb1333d202410609c4ddeae060b3
    Added Reference https://git.kernel.org/stable/c/710866fc0a64eafcb8bacd91bcb1329eb7e5035f
    Added Reference https://git.kernel.org/stable/c/7689ab22de36f8db19095f6bdf11f28cfde92f5c
    Added Reference https://git.kernel.org/stable/c/aa12ee1c1bd260943fd6ab556d8635811c332eeb
    Added Reference https://git.kernel.org/stable/c/de04ddd2980b48caa8d7e24a7db2742917a8b280
    Added Reference https://git.kernel.org/stable/c/ff57186b2cc39766672c4c0332323933e5faaa88
EPSS is a daily estimate of the probability of exploitation activity being observed over the next 30 days. Following chart shows the EPSS score history of the vulnerability.
Vulnerability Scoring Details
No CVSS metrics available for this vulnerability.