CVE-2025-39677

Kernel state corruption via qdisc backlog underflow

Published Sep 5, 2025 · Updated Sep 5, 2025

Incorrect qdisc accounting in the Linux kernel allows local users to corrupt scheduling state via crafted traffic-control limit changes. qdisc_dequeue_internal decrements queue length but omits the matching backlog decrement when it pulls packets from gso_skb, leaving stale bytes that underflow the parent backlog. User-namespace CAP_NET_ADMIN access is sufficient; the underflow can blackhole the device, crash the kernel, or hang qdisc processing.

CVSS severity7.8
High
EPSS probability0.14%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Incorrect qdisc accounting in the Linux kernel allows local users to corrupt scheduling state via crafted traffic-control limit changes. qdisc_dequeue_internal decrements queue length but omits the matching backlog decrement when it pulls packets from gso_skb, leaving stale bytes that underflow the parent backlog. User-namespace CAP_NET_ADMIN access is sufficient; the underflow can blackhole the device, crash the kernel, or hang qdisc processing.

The record

CVE
CVE-2025-39677
Published
Sep 5, 2025
Updated
Sep 5, 2025
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Sep 5, 2025CVE publishedPublication date reported by the CVE source.
  2. Sep 5, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=3.5
  2. Affected versionversion=4b549a2ef4bef9965d97cbd992ba67930cd3e0fe <52bf272636bda69587952b35ae97690b8dc89941
  3. Affected versionversion=4b549a2ef4bef9965d97cbd992ba67930cd3e0fe <a225f44d84b8900d679c5f5a9ea46fe9c0cc7802

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=3.5; version=4b549a2ef4bef9965d97cbd992ba67930cd3e0fe <52bf272636bda69587952b35ae97690b8dc89941; version=4b549a2ef4bef9965d97cbd992ba67930cd3e0fe <a225f44d84b8900d679c5f5a9ea46fe9c0cc7802

Published CVSS scores

5.5NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
7.8LinuxCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
5.5Canonical UbuntuCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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