CVE-2025-39766
What it is
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.
At a glance
- Exploitability
- Can be exploited locally on the machine with a low-privilege account. High risk of data exposure, data tampering, service disruption.
- Exploit odds
- 0.2% chance of exploitation in the next 30 days (EPSS).
- Fix
- A patch, advisory or fixed version is referenced. Upgrade or apply it.
Timeline
- PublishedDisclosed publicly on CVE.org and NVD
- Last updatedMost recent change to the record
Why it ranks here
- Exploited in the wild: no, CISA does not list it.
- Exploit odds: 0.2% in the next 30 days (EPSS).
- Severity: 7.8 HIGH (CVSS).
- Fix: a patch or advisory is linked.
Details
- Published
- Last modified
- Exploit probability
- 0.2% · EPSS, next 30 days
- Record status
- Modified
Affected
- Linux Kernel < 5.4.297
- Linux Kernel < 5.10.241
- Linux Kernel < 5.15.190
- Linux Kernel < 6.1.149
- Linux Kernel < 6.6.103
- Linux Kernel < 6.12.44
- Linux Kernel < 6.16.4
- Linux Kernel 6.17
Attack profile CVSS 3.1 · 7.8
- Attack vector
- Local
- Complexity
- Low
- Privileges needed
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
Raw vector
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Is it in your code?
Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.
Read https://cve-list.com/agent/cve/CVE-2025-39766.md and follow it. Check whether this project is affected by CVE-2025-39766. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.
Fix and advisories
- 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
References
- 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
- https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html
- https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html
- https://cert-portal.siemens.com/productcert/html/ssa-032379.html