CVE-2025-39766In 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 du…
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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.
- CVSS
- 7.8 HIGH (v3.1, NVD)CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- Weakness (CWE)
- Not given
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- Not given
- NVD analysis
- Modified
- Record last updated
- Oct 19, 2026
- First seen by InfoSec Signals
- Oct 19, 2026
Affected products
linux linux_kernel linux:linux_kernel | from 4.19 before 5.4.297; from 5.5 before 5.10.241; from 5.11 before 5.15.190; from 5.16 before 6.1.149; from 6.2 before 6.6.103; from 6.7 before 6.12.44; from 6.13 before 6.16.4; 6.17; and 1 more ranges | NVD |
debian debian_linux debian:debian_linux | 11.0 | NVD |
References
- https://git.kernel.org/stable/c/0dacfc5372e314d1219f03e64dde3ab495a5a25epatch
- https://git.kernel.org/stable/c/15de71d06a400f7fdc15bf377a2552b0ec437cf5patch
- https://git.kernel.org/stable/c/62d591dde4defb1333d202410609c4ddeae060b3patch
- https://git.kernel.org/stable/c/710866fc0a64eafcb8bacd91bcb1329eb7e5035fpatch
- https://git.kernel.org/stable/c/7689ab22de36f8db19095f6bdf11f28cfde92f5cpatch
- https://git.kernel.org/stable/c/aa12ee1c1bd260943fd6ab556d8635811c332eebpatch
- https://git.kernel.org/stable/c/de04ddd2980b48caa8d7e24a7db2742917a8b280patch
- https://git.kernel.org/stable/c/ff57186b2cc39766672c4c0332323933e5faaa88patch
- https://lists.debian.org/debian-lts-announce/2025/10/msg00007.htmlmailing-list, third-party-advisory
- https://lists.debian.org/debian-lts-announce/2025/10/msg00008.htmlmailing-list, third-party-advisory
- https://cert-portal.siemens.com/productcert/html/ssa-032379.html
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.